Morse code encodes letters using dits (dots, .) and dahs (dashes, -). It is a time-based encoding system where a dit represents one unit of time. A dah lasts three units. There is a one-unit pause between each dit and dah within the same letter, a three-unit pause between letters, and a seven-unit pause between words. The tree representation below shows how different letters are encoded using dits and dahs.