Mod

A watch assembled or customized from genuine, legitimately sourced parts — most commonly a Seiko movement (NH35, NH36, VK63) paired with an aftermarket case, dial and hands — built to order by a small workshop rather than mass-produced by the original brand. Distinct from a rep: nothing about a mod claims to be a counterfeit of a specific genuine product.

Source: Standard usage across the Seiko-mod community and the shops profiled in NWBIF's Mods & Homages directory.