Quick definition: A signed addendum to an active job that adds work, removes work, or adjusts pricing — created mid-project when scope changes.
Change orders are how you handle 'while you are here, can you also...' — without doing the extra work for free or losing the customer trust by raising the price verbally.
A clean change order:
In JobPricer (Pro plan), change orders are 1-tap: tap +Change Order, add the lines, customer signs from their phone in the field, balance updates. No more verbal 'we will work it out at the end'.