The document discusses constraint satisfaction problems (CSPs). It defines a CSP as a decision problem that involves making choices without violating constraints. A CSP consists of variables, values for each variable, and constraints on the values. Examples of CSP applications include timetabling, scheduling, and Sudoku puzzles. Solving a CSP involves exploring all possible assignments of values to variables while checking constraints. Backtracking is an important technique for solving CSPs by trying assignments and abandoning ("backtracking") from ones that violate constraints. The document walks through solving the 4-Queens puzzle as a CSP using backtracking.