An extract is a literal copy of a portion of a document. The copy is as faithful to the original as possible. Spelling, grammar, and punctuation are included in their original form even if there are errors or usage that does not match present-day practice.
An extract is not the same as a transcript; an extract includes only a portion of the document whereas a transcript is a copy of the entire document.
Some extraction guidelines can be found at Cole & Altenhoff Genealogy under transcription.