Residual feed intake (RFI) is a term used in the livestock industry to measure feed efficiency. However, there are various synonyms for this term, including dry matter intake, feed conversion efficiency, and feed efficiency ratio. These synonyms are all interconnected as they measure the amount of feed an animal needs to produce a certain amount of weight gain or milk production. Another synonym for RFI is residual intake and gain (RIG), which is commonly used in beef cattle breeding programs. Ultimately, the use of these synonyms helps farmers and researchers to evaluate the feed efficiency of their animals and to make informed decisions about breeding and feeding programs to improve overall productivity.