Stepping (also core stepping or stepping level) refers to a specific revision of an integrated circuit.
Stepping is analogous to software versioning. Following the successful completion of an RTL development, the first silicon tapeout is usually called "A0". Manufacturing enhancements, as well as functional bug fixes, can later be introduced which alters the photomask. Those alterations progressively increment the stepping. Minor changes increment the revision number (e.g., "A1", "A2", and "A4"). Larger changes usually increment the revision letter (e.g., from "A4" to "B0").