Definitions for "on spec"
Keywords:  speculation, editor, hope, writer, idea
Doing a job without any guarantee of being paid, in the hope of winning future business.
Short for "on speculation." This refers to a manuscript written for an editor who has expressed interested in an idea or story, but who is unwilling to buy the piece sight-unseen. The editor doesn't promise to buy your manuscript, but does promise to give it a fair reading.
means the writer was not officially assigned the work by an editor. The editor is not obligated to publish the piece.