Coins earned after completing a wave. Refers to both a workshop stat and a lab.
The Coins/Wave workshop stat as 149 levels with a maximum value of 150.
The Coins/Wave lab increases the increments of workshop levels and the maximum workshop value. You unlock this lab in Milestones by unlocking labs, which you do by reaching Tier 1 wave 30.
The Coins Perk also increases the amount received from Coins/Wave.