A specialty contractor hired by a GC to perform a specific trade or scope on a project.
Subs are the trade-specific workforce — electricians, plumbers, roofers, drywall, paint. They contract with the GC, not the owner, and the GC is responsible for paying them and managing their work.
Strong sub relationships are how GCs scale — a reliable roofer or electrician is worth more than a marginally cheaper one who blows schedule.