1. A rudimentary form of testing applied to electronic equipment following repair or reconfiguration, in which power is applied and the tester checks for sparks, smoke, or other dramatic signs of fundamental failure.
See magic smoke
2. By extension, the first run of a piece of software after construction or a critical change.
See and compare reality check
There is an interesting semi-parallel to this term among typographers and printers: When new typefaces are being punch-cut by hand, a "smoke test" (hold the letter in candle smoke, then press it onto paper) is used to check out new dies.