Re-authenticating
When an authenticated session expires, the user can continue the activity without loss of data after re-authenticating.
In plain language
If someone's login session expires while they're in the middle of something, logging back in should let them continue exactly where they left off — without losing any of their work.
Why it matters
Getting logged out mid-task is frustrating enough; losing everything typed so far on top of that can mean redoing a lot of work, which is especially discouraging for people who already take longer to complete tasks.
In practice
Fails this criterion
A user filling out a long registration form gets logged out partway through, and after logging back in has to start the entire form over from scratch.
Meets this criterion
The same form saves the user's progress, so after re-authenticating, they're taken right back to where they left off with everything they'd already entered still there.
Test it yourself
Fill out a long form or process on the site, then wait for the session to expire (or simulate a timeout). After logging back in, is your progress still there, or do you have to start over?