What is "ringer equivalence number"

n. (context telecommunications English) A number denoting the electrical load of a telephone ringer circuit on a particular line.

The ringer equivalence number (REN) is a telecommunications measure that represents the electrical loading effect of a telephone ringer on a telephone line. In the United States, the REN was first defined by U.S. Code of Federal Regulations, Title 47, Part 68, based on the load that a standard Bell System model 500 telephone represented, and was later determined in accordance with ANSI/TIA-968-B (August 2009).

Although the REN was developed in the United States, analogous measurement systems exist internationally.