n. 1. The largest value that can be represented in a particular type of variable (register, memory location, data type, whatever).
2. 'minus infinity': The smallest such value, not necessarily or even usually the simple negation of plus infinity. In N-bit twos-complement arithmetic, infinity is 2N-1 - 1 but minus infinity is - (2N-1), not -(2N-1 - 1).
Note also that this is different from "time T equals minus infinity", which is closer to a mathematician's usage of infinity.