Email marketing vocabulary.

A/B Testing

Sending two versions of an email to different segments of your list to measure which performs better. In Klaviyo, you can A/B test subject lines, preview text, send times, and content within flows and campaigns.

Attribution Window

The time period after an email click or open during which a purchase is credited to that email. Klaviyo's default is 5 days for campaigns and flows. Shorter windows (1–2 days) are more conservative and typically more accurate.

Abandoned Cart Flow

An automated email (or SMS) sequence triggered when a shopper adds items to their cart but doesn't complete checkout. A 3-email sequence typically recovers 12–18% of abandoned carts.

Active Subscriber

A contact who has opened or clicked at least one email within a defined window, typically 90 or 180 days. Active subscribers are the core of your deliverable audience.

Bounce Rate

The percentage of emails that could not be delivered. Hard bounces (invalid addresses) should be suppressed immediately. A bounce rate above 2% signals a list health problem that will damage your sender reputation.

Browse Abandonment Flow

An automated sequence triggered when a visitor views a product page but doesn't add to cart. Less urgent than cart abandonment, typically a 2-email sequence focused on value and social proof rather than urgency.

BFCM

Black Friday / Cyber Monday. The highest-revenue email period of the year for most ecommerce brands. Requires a campaign plan, segmentation strategy, and deliverability preparation starting in September.

Campaign

A one-time email send to a defined segment or list, as opposed to a flow, which sends automatically based on behaviour. Campaigns are used for promotions, newsletters, announcements, and seasonal sends.

Click-Through Rate (CTR)

The percentage of delivered emails that received at least one click. A more reliable engagement signal than open rate, especially post-iOS 15. Ecommerce benchmark: 1–3% for campaigns, 2–5% for flows.

Click-to-Open Rate (CTOR)

Clicks divided by opens, expressed as a percentage. Measures how compelling your email content is for those who opened. A low CTOR with a high open rate indicates the subject line is strong but the content isn't delivering.

Conditional Split

A Klaviyo flow feature that sends contacts down different paths based on conditions, e.g., VIP vs. non-VIP, purchased vs. not purchased, SMS subscriber vs. email only.

Deliverability

Whether your emails reach the inbox (vs. spam folder or being blocked entirely). Affected by sender reputation, authentication, list health, and engagement rates. The foundation of everything else in email marketing.

DKIM (DomainKeys Identified Mail)

An email authentication method that uses a digital signature to verify that an email was sent from an authorised server. Required for inbox placement with major email providers.

DMARC (Domain-based Message Authentication)

A policy that tells email providers what to do when emails fail SPF or DKIM checks. A properly configured DMARC record protects your domain from spoofing and improves deliverability.

Double Opt-In

A subscription process where a new subscriber must confirm their email address by clicking a link in a confirmation email. Produces a smaller but more engaged list with lower bounce rates.

Email Flow

An automated email sequence triggered by a subscriber action or property, e.g., a purchase, a cart abandonment, or a date. Flows generate revenue continuously without requiring manual sends.

Engagement Rate

A combined measure of opens and clicks as a percentage of delivered emails. High engagement rates signal to ISPs that your emails are wanted, improving deliverability.

ESP (Email Service Provider)

The platform used to send marketing emails. Klaviyo, Mailchimp, Omnisend, and ActiveCampaign are common ESPs. For ecommerce, Klaviyo is the category leader.

Flow Trigger

The event in Klaviyo that starts an automated flow, e.g., "Placed Order", "Started Checkout", "Viewed Product", or a custom event. Choosing the right trigger and filter logic is critical to flow performance.

Frequency Capping

Limiting how often a single contact receives emails within a set time period. Protects against list fatigue and reduces unsubscribe rates, especially during high-send periods like BFCM.

Hard Bounce

A permanent email delivery failure caused by an invalid, non-existent, or blocked address. Hard bounces should be suppressed immediately to protect sender reputation.

Holdout Group

A control segment excluded from email sends to measure the true incremental revenue impact of email marketing. The most accurate way to measure email's true ROI rather than attributed revenue.

Klaviyo

The leading email and SMS marketing platform for ecommerce brands. Integrates natively with Shopify, stores customer behaviour data as profiles, and enables sophisticated segmentation and flow automation.

Klaviyo Profile

A record in Klaviyo that stores all data associated with a customer, email, SMS, purchase history, web behaviour, predicted CLV, and custom properties. The foundation of Klaviyo's segmentation capability.

List Hygiene

The ongoing process of removing or suppressing invalid, inactive, or unengaged contacts to maintain deliverability and improve engagement metrics.

LTV (Lifetime Value)

The total revenue generated by a customer over their relationship with your brand. Klaviyo uses predictive analytics to forecast LTV and enables segmentation by predicted LTV tier.

Open Rate

The percentage of delivered emails that were opened. Post-iOS 15, open rates are inflated by Apple's Mail Privacy Protection (MPP) which pre-fetches emails. CTR and placed order rate are more reliable signals.

Opt-In

The process by which a contact gives permission to receive marketing emails. GDPR and CAN-SPAM require consent-based opt-in. Klaviyo supports single opt-in (immediate subscribe) and double opt-in (confirmation required).

Post-Purchase Flow

An automated email sequence sent after a customer completes a purchase. Covers order confirmation, shipping updates, onboarding/education, review requests, and upsell or cross-sell offers.

Predictive Analytics

Klaviyo's machine learning features that forecast each contact's predicted LTV, churn risk, next order date, and average order value. Enables segmentation by predicted behaviour rather than just historical data.

Preview Text

The snippet of text displayed after the subject line in most email clients. Effectively a second subject line, strongly influences open rate when crafted intentionally.

Revenue Per Recipient (RPR)

Total email revenue divided by the number of recipients. The single best metric for comparing email performance across different list sizes and send volumes. Industry benchmark for well-managed ecommerce email: $0.08–$0.20 per email sent.

Replenishment Flow

An automated email sent when a customer is likely to have run out of a consumable product. Triggered by purchase date + average usage cycle. Highly effective for supplements, skincare, coffee, and repeat-purchase categories.

Segmentation

Dividing your email list into groups based on shared characteristics, purchase behaviour, engagement level, product interest, location, or predicted LTV, to send more relevant, targeted emails.

Sender Reputation

A score assigned to your sending domain and IP by ISPs based on engagement rates, spam complaints, bounce rates, and sending consistency. A damaged sender reputation is the primary cause of inbox placement failures.

SMS Marketing

Text message marketing integrated with email in Klaviyo. Higher open rates than email (98% vs 25–35%) but requires explicit TCPA-compliant opt-in. Most effective as a complement to email, not a replacement.

SPF (Sender Policy Framework)

An email authentication record that specifies which servers are authorised to send email on behalf of your domain. Required alongside DKIM and DMARC for reliable inbox placement.

Sunset Flow

A re-engagement sequence sent to chronically inactive subscribers (typically 6+ months no open or click). If they don't engage, they're suppressed, protecting sender reputation while preserving the contact record.

Suppression List

Contacts in Klaviyo who will not receive marketing emails, because they unsubscribed, hard bounced, or were manually suppressed. Well-managed suppression lists are essential for deliverability.

Welcome Series

An automated email sequence sent to new subscribers immediately after they join your list. The highest-revenue-per-recipient flow for most ecommerce brands. A well-built 5-email welcome series converts 15–25% of new subscribers into first purchases.

Win-Back Flow

An automated sequence targeting lapsed customers, those who haven't purchased in 90–180+ days. A 3-email sequence typically reactivates 5–12% of lapsed customers without discounting.

Zero-Party Data

Data that a customer intentionally shares with a brand, quiz answers, preference centre selections, survey responses. More accurate than inferred data and increasingly valuable as third-party cookies disappear.