Definition
Smoke test refers to the first test made to a system, usually after a release or upgrade, to provide some assurance that the system under test will not catastrophically fail.
Comment
In software testing, smoke testing is a preliminary to further testing, intended to reveal simple failures severe enough to reject a prospective software release.
On many programmes and large projects, testing will take up a significant portion of the budget. But it will receive less management attention than an activity of this size warrants.