Thin Provisioning – The allocation of storage capacity to a volume on a disk or solid state drive when it is actually needed to store data instead of allocating the blocks in advance. An application is told it has , for example, access to a 10TB volume but blocks are only allocated to that volume when data needs to be written. The application sees a virtual, thinly provisioned volume and not a real one. This can be a way of providing more virtual capacity to applications than actually exists on the drive or drives being used.
This is typically done because, when volumes are fully provisioned with blocks, the utilisation rate can be low, meaning that much capacity is wasted.