A clause that gives earlier investors more shares (or a better conversion price) when a later round prices lower, so their stake doesn't get punished by the cheaper round.
WeWork was last valued at $47B in January 2019. By October, after the failed IPO, SoftBank's $9.5B rescue package valued the company near $8B. Earlier preferred holders, protected by anti-dilution clauses, received conversion adjustments that issued them substantially more common stock at the new price, while founder and employee equity took the full brunt of the markdown.