Codebook learning

Hello, I need your help.
I was read journal about codebook learning. The journal say encoded feature by codebook learning. Please help, what is mean about encoded codebook learning ?

Codebook learning is a powerful technique of signal representation and encoding used in many ares of computer vision (image enhancement, denoising, compression etc). Google “K-SVD” for example of sparse coding.
There are few approach that allow to use codebooks in DL frameworks for example: VQ-VAE , and Memory Networks

Hope it will help.