Cookies are small text files a website stores in your browser so it can remember you between requests and visits. They hold things like a login session, items in a cart, a language choice, or an anonymous ID that analytics tools use to recognize a returning visitor.
A first-party cookie is set by the site you're visiting — it keeps you logged in or remembers your cart. A third-party cookie is set by another domain loaded on the page, typically an ad network tracking behavior across sites. Browsers now block most third-party cookies by default, which is reshaping how advertising and cross-site analytics work.
A session cookie disappears when you close the browser, which suits a checkout flow. A persistent cookie stays for a set lifetime — say 30 days — so a site can remember your preferences or attribute a later purchase to an earlier visit.
Directly, no — Googlebot and other crawlers fetch pages without accepting cookies, so gating content behind a cookie wall can hide it from search entirely. Indirectly they matter through page speed, measurement, and compliance, which is why cookie handling belongs in your technical SEO checks: