Invoicing in stages as work is completed, instead of billing only at the end of the job.
Progress billing matches your invoice cadence to your actual work and cost outflow. On longer jobs it's the difference between getting paid as you go and floating the project on your own credit card.
AIA G702/G703 is the standard commercial form — every line item of the schedule of values shows the contract amount, work completed to date, retainage, and current amount due. Residential progress bills can be simpler — milestone-based on the draw schedule works fine.