Prime Contract
The direct contract between the owner and the general contractor (or design-builder, or CM at risk), the main agreement everything else on a project, including every subcontract, ultimately flows from and has to be consistent with.
Why it matters
Every subcontract is supposed to "flow down" the relevant terms of the prime contract, so a subcontractor is bound by many of the same obligations the GC agreed to with the owner. Understanding what's actually in the prime contract is often the starting point for resolving a dispute anywhere else on the project.
On a real project
A prime contract between an owner and general contractor includes a strict notice requirement for any delay claim. That same notice requirement gets written into every subcontract too, so a subcontractor's late notice of their own delay can jeopardize the GC's ability to pass that claim up to the owner.
Who this matters most to
A Contracts Administrator makes sure every subcontract properly flows down the prime contract's key terms rather than leaving gaps. A Project Manager refers back to the prime contract constantly when a dispute or change comes up, since it's the ultimate source of what the GC actually agreed to.
Where this goes wrong
A general contractor signs subcontracts that don't flow down a strict notice requirement from the prime contract. A subcontractor's delay isn't reported in time under the prime contract's own deadline, and the GC loses the ability to pass a legitimate delay claim up to the owner, a gap created entirely by an incomplete flow-down of the prime contract's terms.