Coupler is a word used to describe any of a number of things:
- A railway coupling device;
- A Janney coupler;
- An electronic device, more properly, an acoustic coupler;
- A telecommunications device known as a directional coupler;
- A kind of laser mirror known as an output coupler;
- A connector between two moving parts to relay the motion, such as a Universal joint or an Oldham coupler.
- A device used on a pipe organ or harpsichord to allow a player to play multiple divisions at once, by means of "coupling" a division to another at either sub, super, or octave pitches;
- A valve, specifically a tap, for controlling the release of beer out of a keg;
- A short length of pipe with two female threads, see coupling (piping);
- A sound artisu coupling (sound);
- A quick coupler used in construction machines to allow the rapid change of buckets;
- The name given to the floating link in a Four-bar linkage
- Coupler is a data toll that allows coupling of data from different sources. Used in Electronic Data Exchange (EDI). Example is Microsoft Biztalk Server and eLife Coupler.