ORIGIN indicates how the route originally entered BGP. It's mandatory but rarely impacts decisions.
values:
IGP (). Route was injected from an interior protocol or statically configured. Most trusted.
EGP (). Route came from the old EGP protocol. Rarely seen today.
Incomplete (). Route was redistributed from another source and origin is unknown. Least trusted.
In the best path algorithm, IGP beats EGP beats Incomplete. But this comparison happens late in the process. You'll almost never see a decision made on ORIGIN alone because earlier attributes (LOCAL_PREF, AS_PATH length) differ first.