A number has stepped digits when its digits form an arithmetic progression — each digit differs from the previous one by the same fixed amount — with a gap of at least 2. Examples: 2468 and 8642 (gap 2), 13579 (gap 2), 147 and 369 (gap 3), 159 (gap 4), and 9630 (gap −3).
A gap of 1 is excluded because that's just a plain run of [[consecutive-digits]], and a gap of 0 is a [[repdigit]]. What's left are the genuine ‘equal-skip’ patterns: the even-digit ladder 02468, the odd ladder 13579, multiples-of-three 0369, and their descending mirrors.
These sit alongside [[ascending-digits]] and [[descending-digits]] in the digit-pattern family — a stepped number is always monotone, but most monotone numbers aren't evenly stepped.