This document provides an overview of nondeterministic finite automata (NFAs). It begins by explaining how NFAs relax the requirement in deterministic finite automata (DFAs) that there be exactly one transition from each state on each input symbol. An NFA may have multiple possible transitions from a state on a given symbol. The document then discusses how NFAs use nondeterminism and spontaneous transitions to define the languages they accept. It introduces the concept of instantaneous descriptions to formally define how an NFA transitions between configurations and accepts strings. The language an NFA accepts is the set of strings where at least one sequence of transitions reaches an accepting state.