A persistent cookie is one with an expiry: it survives the browser being closed and is sent again on the next visit, until the date arrives or somebody clears it. A session cookie has no expiry and is dropped when the session ends. That is the entire technical difference, and it is written by whoever sets the cookie rather than configured anywhere on your site.
How the two are actually set
Both come from the same response header or the same script call. Adding an Expires date or a Max-Age in seconds makes the cookie persistent; omitting both makes it a session cookie. Nothing else in the header changes the classification. This matters when you audit, because the only reliable way to know which of yours are persistent is to read the attributes the browser recorded rather than to consult a vendor's documentation.
What browsers do to the number you asked for
Requested lifetimes are increasingly treated as an upper bound rather than a promise. Cookies written by scripts in the page are capped more aggressively than those written by the server, and anything that looks like a cross-site identifier may be shortened, partitioned or refused. So a persistent cookie in your table with a two year lifetime may be a much shorter cookie in a real visitor's browser, and the table should record what was observed.
Why persistence is not the consent question
People reach for lifetime as a proxy for intrusiveness, and it is a poor one. A session-length analytics identifier needs consent; a persistent language preference the visitor chose may not. The test is whether the storage is strictly necessary for the service requested, and how long it lasts is a separate fact that belongs in the disclosure rather than in the classification.
Questions people ask about persistent cookies
How long can a persistent cookie last?
As long as the expiry asks for and the browser allows, and the second half of that sentence has been doing more of the work every year.
Is the consent cookie persistent?
It has to be, or the banner reappears on every visit. It is also strictly necessary, because the site cannot honour a decision it cannot remember.
Do persistent cookies survive a device restart?
Yes, until the expiry or a clear. That is the point of them.
Does clearing cookies withdraw consent?
It removes the record on that device, so the banner will ask again. Whether it withdraws the consent you stored server side depends on how you built the record, which is a question worth answering deliberately.
Should I shorten my cookie lifetimes?
Where you control them and nothing needs the longer window, yes. It is a small, cheap reduction in what you are holding, and it is easy to explain.