白车身的定义：白车身（Body in White）是指完成焊接但未涂装之前的车身，不包括车门、引擎盖等运动件。白车身加上内外饰（包括仪表板、方向管柱、座椅、前后挡风玻璃、后视镜、翼子板、水箱、大灯、地毯、内饰护板等等）及车门、引擎盖、行李箱盖和电子电器系统就组成真正意义上的车身，行内称为trimmed body，意即装好的车身，在此基础上再加上底盘（包括发动机、变速箱、传动系统、制动系统、悬架系统、排气系统等）就组成了整车。以下是维基百科对白车身的定义：

Body in white or BIW refers to the stage in automotive design or automobile manufacturing in which a car body's sheet metal components have been welded together — but before moving parts (doors, hoods, and deck lids as well as fenders) the motor, chassis sub-assemblies, or trim (glass, seats, upholstery, electronics, etc.) have been added and before painting.

The name derives from manufacturing practices before steel unibody or monocoque bodies — when automobile bodies were made by outside firms on a separate chassis with an engine, suspension, and fenders attached. The manufacturers built or purchased wooden bodies (with thin, non-structural metal sheets on the outside) to bolt onto the frame. The bodies were painted white prior to the final color.