A talent pool is every candidate you have ever collected in one place: applicants from past roles, referrals, people you sourced, anyone whose details you kept. In theory it is one of the most valuable assets a hiring team owns, a ready supply of people you have already found and often already assessed.
In practice, its value depends entirely on one thing: whether you can actually search it. A pool you can query by skill, role or experience is something you reach into the moment a role opens, and it becomes your fastest source of hires. A pool you can only scroll is a pool nobody looks at, and it quietly turns into a graveyard of good people you will never contact again.
The difference between the two is not the number of candidates in it but how easy it is to get value back out. That is why a useful talent pool has to be searchable and clean, with one record per person and enough context attached to know why each one mattered. Storage is not the same as a tool, and only a tool gets used.