Abacus is a simple mathematical tool used for counting and calculating. It is one of the oldest calculating instruments still in use today, with a history dating back to ancient Egypt and China. Abacus consists of a frame with beads or other counters that can be moved up and down along rods. Each bead represents a digit and can be moved from one side of the frame to the other to represent a number. The abacus can be used to add, subtract, multiply and divide.