Deca, short for decagram, is a metric unit of mass equal to ten grams. It is part of the International System of Units (SI) and is commonly used in scientific contexts to measure small quantities of substances. The prefix "deca-" comes from the Greek word "deka," meaning ten. In addition to mass, the term "deca" can also refer to decameter, a unit of length equal to ten meters. This unit is often used in fields like geography and engineering to describe distances. Both decagram and decameter are part of the metric system, which is widely used around the world for its simplicity and ease of conversion.