The Free On-line Dictionary of Computing (30 December 2018):

Emitter Coupled Logic

   (ECL) (Or "Current Mode Logic") A technology for building
   logic gates where the emitter of a transistor is used as the
   output rather than its collector.  ECL has a propagation time
   of 0.5 - 2 ns (faster than TTL) and a power dissipation 3 -
   10 times higher than TTL.

   (1994-11-09)