Simple definition
A VMware delta disk records virtual disk changes associated with a snapshot while its parent disk remains unchanged.
Purpose and use
A VMware delta disk retains writes associated with a snapshot state without rewriting the complete parent disk.
How does it work?
Reads combine delta and parent information according to the dependency chain.
Example and verification
Monitor file growth and free capacity while a backup retains a snapshot.
Points to watch
Manually deleting a delta can make the chain unusable. A delta alone replaces neither its parents nor a backup.
In short
A delta is a disk-chain dependency rather than a standalone VM copy.