Summary: One of natural measures of the complexity of a term is the length of term, the total number of both operation symbols and variables that occur in the term. Based on the usual superposition operation and the generalized superposition operation of terms, two significant formulas for counting the length of terms in these operations are established. We also define a novel class of terms which is called terms of a fixed length. The partial superposition for such terms is proposed under a suitable condition and the partial algebra of terms of a fixed length is constructed.