Effective character level

An effective character level (ECL) is a number that represents a creature's overall power relative to that of a character from the Player's Handbook. A creature with an effective character level (ECL) of 10 is roughly equivalent to a 10th-level character. A creature's ECL is the sum of its hit dice (including class levels) and level adjustment.

For instance, a splinterwaif has 2 HD and a +4 level adjustment. It is the equivalent of a 6th-level character.