Term frequency is the measurement of how frequently a term occurs within a document. The easiest calculation is simply counting the number of times a word appears. However, there are ways to modify that value based on the document length or the frequency of the most frequently used word in the document.
The problem with using raw word frequency is that relevance does not increase proportionally with usage. For this reason, the log frequency weight of the term is often used.
Term frequency is one component of Term Frequency – Inverse Document Frequency.