A quick search on Google returns this:
"A regular array of identical finite state automata whose next state is determined solely by their current state and the state of their neighbours. The most widely seen is the Game of Life in which complex patterns emerge from a (supposedly infinite) square lattice of simple two state (living and dead) automata whose next state is determined solely by the current states of its eight closest neighbours and itself." - http://www.cs.ucl.ac.uk/staff/W.Langdon/gpdata/glossary.html
In Roguelikes, cellular automata might provide a tool during map building, for instance to dig out cave-like rooms or spawn vegetation. ADOM uses a variant of Conway's Game of Life to decide herbal growth patterns.