Definition
Organic traffic is visits that arrive from unpaid search results, as opposed to ads. In GA4 it's the Organic Search channel.
What changes it
Rankings, the number of searches for the topics you cover, and how often results are answered without a click (see zero-click search). AI assistants are a growing alternative to search; their visits are a separate channel, and many arrive without a referrer.
Measuring its value
Judge organic traffic by the sign-ups and retained customers it brings, not by visits alone. Count people, not page loads: crawlers and automated browsers inflate visit counts.