The record date is the company's snapshot. It applies to dividends, to voting-rights at the annual-meeting, to a rights-issue entitlement, and to who receives shares in a spin-off. The transfer-agent works from this list.
Because most investors hold in street-name, the registered holder is usually cede-and-co, and your broker allocates the entitlement to you from its own books.
Example: a company sets a record date of 20 March for a 12 May annual-meeting. Someone who buys on 1 May owns the stock at the meeting but cannot vote, because the register was closed six weeks earlier.
Related: ex-dividend-date, payment-date