To onboard a user or onboard a partner is to set up all the necessary user accounts, permissions, workflow definitions and other elements necessary to engage in electronic transfers of information with those users and partners.
Automatic onboarding of users or partners usually involves external authentication technology of some kind. When that technology involves particularly rich user or partner profiles and allows users and partners to maintain their own information, then the external authentication technology used to onboard users and partners is often called “Community Management” technology.
“On board” and “on-board” are also occasionally used instead of “onboard”, and administrators often use the phrases “onboard a user” and “provision a user” interchangeably. See “provisioning” for more information.