48 C.F.R. § 15.001
As used in this part-
Deficiency is a material failure of a proposal to meet a Government requirement or a combination of significant weaknesses in a proposal that increases the risk of unsuccessful contract performance to an unacceptable level.
Proposal modification is a change made to a proposal before the solicitation closing date and time, or made in response to an amendment, or made to correct a mistake at any time before award.
Proposal revision is a change to a proposal made after the solicitation closing date, at the request of or as allowed by a contracting officer, as the result of negotiations.
Weakness means a flaw in the proposal that increases the risk of unsuccessful contract performance. A "significant weakness" in the proposal is a flaw that appreciably increases the risk of unsuccessful contract performance.
48 C.F.R. §15.001