built, done, bought, etc., as a speculation: the construction of spec houses.
verb (used with object), spec'd or specked or specced, spec'ing or specking or speccing.
to provide specifications for: Their newest truck was spec'd by a computer.
on spec, made, built, or done with hopes of but no assurance of payment or a sale; without commitment by a client or buyer: ad illustrations done on spec; luxury homes built on spec and sold before completion.
Done on a speculative basis; with no assurance of profit. For example, We didn't design our house; the builder built it on spec. The use of spec as an abbreviation for speculation dates from the late 1700s.