Unit propagation is a technique used in Boolean satisfiability (SAT) solving. It involves simplifying a logical formula by identifying clauses that contain only one unassigned variable, known as a "unit clause." When a unit clause is found, the value of its variable can be determined, which helps reduce the complexity of the problem. As the solver assigns values to these variables, it may lead to further unit clauses, allowing for additional deductions. This process continues until no more unit clauses can be found, or a contradiction arises, helping to efficiently narrow down possible solutions in SAT problems.