By default, each proxied request to scrape a webpage gets assigned a different, random IP address every time. But you can choose to reuse the same IP address to launch multiple connections to the same website. This is called a session.
It’s an optional parameter you can set when you connect to an Apify proxy. Your IP address will then be assigned a session ID. Sessions are available for datacenter and residential proxies, but not for Google SERP proxies.