An aperiodic finite-state automaton is a finite-state automaton whose transition monoid is aperiodic.
A regular language is star-free if and only if it is accepted by an automaton with a finite and aperiodic transition monoid. This celebrated result of algebraic automata theory is due to Marcel-Paul Schützenberger.[1]
An aperiodic automaton satisfies the Cerny conjecture.[2]