In data compression, vector quantization is a technique (usually lossy) in which the basic idea is to code a multidimensional vector space into a discrete subspace of lower dimension. The lower-space vector requires less storage space and the data is thus compressed. The transformation into the subspace is usually achieved through projection, or by using a codebook. In some cases, the codebook can be also used to entropy code the discrete value by providing a prefix coded variable-length value.