What "edition of 50" actually means

An edition number — 12/50, say — is shorthand for a contract between the artist, the printer and the eventual owners. The number on the left is the impression order; the number on the right is the size of the formal edition. What that contract guarantees varies. In strict practice it means the plate or screen will be destroyed (or definitively marked) once edition 50 ships. In looser practice it means the artist promises not to print another formal run — but reserves the right to make artist's proofs (AP), printer's proofs (PP), and hors-commerce (HC) impressions, typically 10-15% on top of the edition. When buying an edition, ask the seller to confirm: is this an open edition, a strict edition, or an edition with proofs? Provenance gets cleaner the more specific the answer.