A nondeterministic finite automaton (NFA), or nondeterministic finite-state machine, is a finite-state machine that does not need to obey the restrictions set by DFA, where each of the transition is uniquely determined by its source state and input symbol, and reading an input symbol is required for each state transition. In particular, every DFA is also an NFA. Sometimes the term NFA is used in a narrower sense, referring to an NFA that is not a DFA, but not in this article.