A talent pool is usually held in an applicant tracking system or CRM and grouped by skills, location or role family. It might include strong runners-up from past campaigns, people who registered interest on the careers site, former employees and sourced profiles. Keeping it useful means updating records, noting consent and tagging people clearly, so a recruiter can search it quickly when a matching role opens.
A healthy pool shortens time to fill and reduces advertising spend, because some candidates are already known and partly assessed. It needs care, though. Under data protection law in the UK and EU, people should know their details are kept and for how long, and stale records should be removed. Re-screening pooled candidates against each new role's criteria keeps matches fair and current.