Acts as a hp battery for the party. Usually by having a large pool of hp, and ways to mitigate damage, and keep attacks focused on them, but can also include "vampiric" effects, redirecting damage, reusable self heals, and such.

The classic armored paladin with a shield and feats to prevent movement, but also the summoner who focuses on slow effects, and redirects damage to their summoned companions. Especially if they can redirect from the other PCs.

In most TTRPGs I believe this requires synergy between the players and with the exception of some games no party will succeed with players trying to be purely a role.

Tank: handles/mitigates damage done to party

Healer: restores energy or resources used

Striker: makes sure damage is maximized to target(s)

Support: increases the effectiveness of the other roles.

For Pathfinder and dungeons and dragons I feel you need to pick your two primary roles and a third role if you're trying to adopt roles, but figuring out how you can add to all four is your best bet.