What Does Extraction,transformation,and Loading Mean

What does extraction,transformation,and loading mean?

A) It is a process of entering data,tracking data,and loading it into a database
B) It is a process that extracts information from internal and external databases,transforms it using a common set of enterprise definitions,and loads it into a data warehouse
C) It is a process that is performed at the end of the data warehouse model prior to putting the information in a cube
D) It is a process that is performed at the beginning of the data mining model