In order to obtain the lens you want, or to design the lens desired by a customer, the lens must be thoroughly specified. Not only that, but the specifications must be understood the - same by all parties involved. Unfortunately, even though most terminology related to lens specifications and tolerances is well defined, there is still much ambiguity and lack of care in the use of these terms. In addition, there are many terms that are not universally used with a single meaning. This paper discusses some of the ambiguities and inconsistencies, with the aim of emphasizing the need for adequate definitions and standardized usage of optical terminology.