A Non-deterministic Finite Automaton (NFA) is a theoretical model used in computer science to represent and analyze the behavior of certain types of computational systems. Unlike deterministic finite automata (DFAs), NFAs can have multiple possible transitions for a given input symbol, allowing for more flexibility in state transitions. This means that from a single state, an NFA can move to several different states simultaneously. NFAs are often used in the design of regular expressions and lexical analysis in programming languages. They can be converted into equivalent DFAs, which are easier to implement in software. Despite their complexity, NFAs are valuable for understanding the foundations of automata theory and formal languages.