What is a cookie window?
The period after someone clicks your link during which a resulting sign-up is still credited to you.
When someone clicks a partner link, a cookie records the referral. The cookie window is how long that record stays valid — commonly 30, 60 or 90 days.
Why it matters
People researching where to put money rarely decide the same day. In a market where a reader might compare venues for weeks, the difference between a 30-day and a 90-day window is a large share of your conversions. Two further details decide whether the window is worth what it looks like: whether attribution is last click or first click, which determines who wins when a user clicks several affiliates; and how the operator handles a user who signs up on a different device, since cookies do not follow people across devices and many programs simply lose those referrals.