adjective 3.built, done, bought, etc., as a
speculation:
the construction of spec houses.
verb (used with object) 4.to provide
specifications for:
Their newest truck was spec'd by a computer.
Idioms 5.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.