A repurchase right can mean different things - you'd need to go to the specific language to really determine what it means. In the case of Sam Altman's founder

A repurchase right can mean different things - you'd need to go to the specific language to really determine what it means. In the case of Sam Altman's founder-friendly term sheet, what you're describing is covered by the 'ROFR/Co-Sale Agreement' section. The repurchase right here refers to what happens if a founder leaves before their four-year vesting schedule is up - the company has the right to repurchase their unvested stock, almost certainly (although his term sheet doesn't specify) at the original near-zero issue price. Since founders typically own 100% of their stock for tax purposes (hold it for a year, only have to pay long-term instead of short-term capital gains), the only way companies can subject founders to a vesting schedule is to have the option of buying the unvested portion back.