A unit of measurement used to determine the sexual willingness of a random partner. Often referred to in the context of a verb, a 'Kelso' is equivalent to a full measure. A half-Kelso would suggest that an experience has been only somewhat satisfying. Example: She sucks, but does not swallow, she is only 'Half a Kelso', She enjoys one or more digits inserted into her anus but is not a fan of full penis penetration up the pooper, she is only 'Half a Kelso'. Alternatively, if the sexual experience can be likened to a hardcore porn movie, you would use the verb to describe the situation of having gone all 'Kelso' on her ass.