What is database normalization and denormalization?

Database normalization is the process of restructuring relational data using normal forms for reducing data redundency.

Normalizaion

We can do the normalization using the normal forms. Following is a good example video of 1st, 2nd, 3rd and 4th normal forms.
https://www.youtube.com/watch?v=UrYLYV7WSHM

Denormalizaion

The denormalization is to keep all data in one place and no relational tables. It has drawbacks like query performace will be bad for large dataset. It has few advantages too. One of the advantages is we can avoid complex relational query as all the data are in one place.