The point of the OGL is so you can include or reference things from the System Reference Document in your publication.

EDIT: I realize people might not know what an SRD is. It's basically the bare-bones document explaining the game and its mechanics with all the IP-encumbered names filed off. D&D 5E has an SRD (copy: https://www.5esrd.com/) which 3PPs use when making their own content for the system.