A Boolean circuit whose current output depends only on its current input, with no stored state or feedback dependency. Its delay is bounded by the longest input-to-output path of logic gates. This differs from a synchronous sequential circuit, whose output can depend on state stored at earlier clock edges.
Combinational logic refers to a type of digital logic circuit whose output is a pure function of the present state of its inputs. In other words, the output at any given time depends only on the combination of inputs at that same time, without any memory of past inputs. This is in contrast to sequential logic, where the output depends on both the current inputs and the state of the system (which may be influenced by past inputs).
New to topics? Read the docs here!