A “spec script” is a movie written on “speculation” — without a deal or sale already in place, and without being commissioned.
A writer is not paid to write a spec. She does it on her own time with the hopes of selling it to a buyer, or to use as a writing sample.
In television, “spec” usually refers to a writer’s sample script for an existing television show. An aspiring comedy writer might write a sample episode of a highly-rated comedy currently on the air. His intention is not to get this script produced, but rather to show his comedy writing ability and get staffed on a different show.
Young Hollywood writers’ portfolios usually contain two to three spec features, as well as a few television samples.
Throughout the 1990s and 2000s, spec scripts were a primary factor in hiring decisions for television writers rooms. In recent years, network executives and showrunners are increasingly asking to read “spec pilots,” which — much like a spec feature — are original pilot scripts written without a deal or sale in place and without being commissioned.
Most spec pilots are not purchased or produced, but there are exceptions. Matt Weiner wrote Mad Men as a spec pilot in 2000. As a writing sample, it helped him get hired on The Sopranos. Only after The Sopranos ended did Mad Men get made.