The chuck is the part of the cordless drill driver that holds accessories such as drill or screwdriver bits.
The type of chuck found on a cordless drill driver is known as a keyless chuck. It has 3 jaws which can be opened up to accept bits and closed to hold them firmly in place.
It’s called a ‘keyless’ chuck, because, unlike older models, it does not require a key to open and close the jaws. Instead, this is done by turning part of the chuck manually.