Abacus/ˈæbəkəs/ Definition 1 of 2Pro Tip 1/3Calculation Device An abacus is an ancient counting device, not a modern calculator. Back in my grandmother's school, every student had an abacus. Pro Tip 2/3Physical Interaction Using an abacus involves manually moving beads; it's tactile. I learned basic arithmetic by sliding beads on an abacus. Pro Tip 3/3Historical Importance The abacus was essential before digital calculators; it's a piece of history. The museum's math exhibit features an ancient Roman abacus.