Algebraic notation is the most commonly used notation system in chess today. It uses letters to represent the files (columns) of the chessboard, from a to h, and numbers to represent the ranks (rows), from 1 to 8. Descriptive notation, on the other hand, was widely used in the past but is now less common. It describes the squares based on their relation to the player, such as 'Queen's Bishop 3' (QB3) instead of 'b3' in algebraic notation. Algebraic notation is generally considered more efficient and easier to understand.