The expression "tan(A - B)" represents the tangent of the difference between two angles, A and B. It is a trigonometric function that can be calculated using the formula: tan(A - B) = (tan A - tan B) / (1 + tan A * tan B). This formula helps in finding the tangent of the angle resulting from subtracting one angle from another. Understanding "tan(A - B)" is useful in various fields, including mathematics, physics, and engineering. It allows for the simplification of complex trigonometric expressions and is essential in solving problems involving angles in triangles and periodic functions.