In architecture, engineering, and construction, “spec” is a slangy, informal word that is completely understandable in spoken language, but sometimes muddles meaning when used in business writing.
In a construction project context such as a meeting or a phone call, it’s easily understood when you say “I’ll spec a coiling steel door”, or “Include an allowance for face brick in the spec”.
In the first case, it’s clear that spec means specify. In the second case, it’s clear that spec means specifications.
But things get clumsy when you try to use “spec”, and variations of it, in writing.
When you write “specs” in a sentence, the reader may have to pause to figure out whether the intended meaning is “specifies” or the plural of “specifications”.
And it gets even odder with the use of past tense. Instead of saying “specified” writers will sometimes resort to “specd”, “spec’d”, “speced”, or funniest of all “specked.” In each case, the reader has to pause to figure out what the writer means.
Do yourself and your readers a favor: In written communication, use the full words “specify” and “specifications.”