what is normalization and tell us why it is 3NF?

this is all the list of my tables according to this tell me what is normalization and why it is 3NF    

 

Data Tables: 1. Administrator Table: Fields a id a name gender Data Type int(5) Relationships Primary Key Varchar(20) Not Null Varchar(10) Not Null 2. Doctor Table: Fields Data Type Doctor id int(5) Relationships Primary Key Doctor name Varchar(15) Not Null Dept Varchar(15) Not Null a_id Int(5) Foreign Key