Square wave, triangle wave etc. not defined in International Electrotechnical Vocabulary (IEV.) Are they not standard terminology?
The IEV is intended as a resource for those who prepare standards for the use of electrical and electronic equipment.  It is not intended as a comprehensive vocabulary of electrical engineering. It does include many terms describing pulsed signals of which a square wave is a special case. One must conclude that, up to this time, there has been no need to define such terms in order to generate their technical standards.