Full definition
Rotating sessions are the default for most proxy providers. Every HTTP request you make goes out from a different IP, drawn at random (or round-robin) from the provider's pool. This is what you want for high-volume scraping where each request can be independent — Google SERP queries, product page scraping, broad crawls.
The implementation typically requires no special parameters: you just hit the provider's gateway endpoint and it picks a random IP automatically. Some providers let you tune the rotation: per-request, per-N-requests, or time-based.
Don't rotate when you need session state. If you're logging into a site, navigating multiple pages, or completing checkout, every new IP looks like a different person to the destination — which destroys your session. Use sticky sessions for those.