INTRODUCTION A set of definitions of basic waveguide terms prepared by the Technical Committee on Antennas and Waveguides was published as IRE Standards in December@ 1953 (53 IRE 2. SI). The present Standards on Waveguide Components@ Definitions of Terms@ represent an extension of the work of this committee from 1953 to 1955. Waveguide component terms have not previously been standardized by the IRE; however@ with continuing development in this field the need for such definitions has become increasingly apparent. The present list comprises only the more general@ basic and established terms. For example@ Waveguide Transformer is defined but the many specific types of waveguide transformer such as Double Stub Transformer@ Quarter-Wave Sleeve Transformer@ Probe Transformer@ Eccentric Line Transformer@ and others are not defined. As used in the following definitions@ Waveguide is a generic term which includes transmission line and uniconductor waveguides as special cases. For specific definitions see S3 IRE 2. SI.