The term 'abacus units' can be solved by the word 'BEADS', which is a five-letter word. BEADS are small, round objects that are often used in jewelry making, crafts, and other decorative items. They can also be used as counting tools on an abacus, which is an ancient counting device consisting of a frame with rods on which BEADS are strung. The BEADS are moved along the rods to represent numbers, allowing calculations to be performed.