An accumulator is a type of register included in a CPU. It acts as a temporary storage location which holds an intermediate value in mathematical and logical calculations. Intermediate results of an operation are progressively written to the accumulator, overwriting the previous value. For example, in the operation "3 + 4 + 5," the accumulator would hold the value 3, then the value 7, then the value 12. The benefit of an accumulator is that it does not need to be explicitly referenced, which conserves data in the operation statement.
In modern CPUs, accumulators are replaced by general-purpose registers because they offer more flexibility. However, accumulators may still be in some special-purpose processors.