CRO Glossary
Feature Flag
A code-level toggle that lets teams turn a feature or variant on or off for specific users without deploying new code.
A feature flag (or feature toggle) is a conditional switch in the codebase that determines whether a given user sees a new feature, design, or experience. Experimentation platforms build on top of feature flags to control traffic allocation — assigning some percentage of users to see variant A and the rest variant B — and to roll changes out gradually or roll them back instantly if something breaks, without needing a new deployment.
Beyond experimentation, flags are also used for staged rollouts (releasing a feature to 5% of users, then 25%, then 100%) and for kill switches during incidents. For CRO specifically, the important nuance is that flags must be evaluated consistently per randomization unit — the same user should keep seeing the same variant across sessions, or the test's data becomes unreliable.
Example: a team wraps a new checkout flow in a feature flag, allocates 50% of traffic to the new flow, and monitors guardrail metrics. When a payment bug is discovered mid-test, they flip the flag off for all users within minutes rather than waiting for an emergency deploy.
Related terms
Above vs Below Median Split
A segmentation technique that divides users into two groups at the median of a metric to compare high and low engagers.
Qualitative Feedback Loop
A recurring process of collecting and acting on user comments, session recordings, and survey responses to inform test hypotheses.
Experiment Metadata
The structured record of who, what, when, and how for a test — hypothesis, owner, dates, variants, and metrics used to track and audit it.
Pre-Test Analysis
The upfront work of validating traffic, metrics, and baseline data quality before launching an experiment.
Above-the-Fold vs Below-the-Fold Messaging Hierarchy
How the order and prominence of value-proposition messaging is split between the visible screen and the rest of the page.
Experiment Contamination
When a control or variant group is unintentionally exposed to the other condition, corrupting the comparison.
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