Several ambiguities in the present terminology of behavior theory obscure some important theoretical assumptions and experimental details in current research. Left unclarified, such ambiguities impede the accurate analysis of laboratory procedures, and prevent reliable communication among researchers. This paper focuses on the term "schedule of reinforcement". It points out that two distinguishable operational rules are implicated in the term: in the case where reinforcement is of the so-called response contingent type, the "schedule" is really a rule to identify the response to be reinforced; in the case of non-contingent reinforcement, the "schedule" is truly a rule for delivery of reinforcement. Other terminological ambiguities that are encountered in a discussion of this term include "reinforcement" and "intermittency." A resolution of these problems will necessarily involve the procedures of non-contingent reinforcement, and the parameter of reinforcement probability.