Register
Register turns up in 2 fields: HVAC, printing. Here is what it means to the people in each one.
Register in HVAC
A supply or return grille fitted with a damper so its airflow can be adjusted or shut off.
Trade usage splits the outlet family three ways: a grille is just a face with fixed or adjustable bars, a register is a grille with a damper behind it, and a diffuser spreads air in a pattern. Residential floor and wall supplies are usually registers, and the damper lever lets a balancer trim the flow to each room.
"Half the registers in the house are closed, that's why the static is through the roof and the coil keeps icing."
Register in printing
The precise alignment of multiple printed layers or colors on a single sheet.
In printing, register is the exact physical alignment of differing plates, colors, or front-to-back impressions. When a job is in register, the cyan, magenta, yellow, and black inks overlap perfectly to form a sharp image without blurry edges or color halos. A secondary, historic meaning refers to the inner alignment part of a typecasting mould.
"The magenta plate is slightly out of register, giving all the photos a fuzzy red shadow."