Epsilon-NFA

Summary

An $\varepsilon$-NFA is a nondeterministic finite automaton that may also change state without reading any input symbol, by an $\varepsilon$-move. These free moves make it easy to glue automata together, which is why they appear in the standard translation of regular expressions into automata. Every $\varepsilon$-NFA can be turned into an NFA without $\varepsilon$-moves, and then into a DFA, that accepts the same language. So $\varepsilon$-NFAs accept exactly the regular languages.