A Karnaugh map is a graphical representation of a logic system that can be used to minimize sum-of-products or product-of-sums Boolean expressions. It works by plotting the minterms or maxterms of a function onto a grid whose dimensions correspond to the number of variables. Ones are placed in the cells that correspond to true minterms or false maxterms, while don't cares are marked with Xs. By grouping adjacent ones, the Karnaugh map allows identifying logical patterns to minimize the expression into prime implicants. The document provides examples of two, three, and four variable Karnaugh maps and discusses their use case for minimization.