There are multiple definitions - click on the translation that matches your context.

车牌

名词

full

registration number

noun

Definitions of registration number

an official number that is given to you when you have information recorded officially

The car's registration number was reported to police.

the official combination of numbers and letters that motor vehicles in most jurisdictions must display on a car registration number plate before they may be driven on a public highway

You'll need the vehicle's registration number.