A PST file is a Microsoft Outlook Personal Storage Table archive. It can store emails, calendar items, contacts, tasks, and attachments in one file, often used for local backup or export of mailbox data.
In cyber security, PST files matter because they can contain large amounts of sensitive communications and embedded files. Attackers may steal PSTs during intrusion, then search them for credentials, internal plans, or documents. Defenders also use PSTs during incident response to preserve and review mail evidence, but they must handle them carefully because a single archive can expose years of correspondence and attachments.