What is a normalized/canonical url?

Caching depends upon this...
Q: What is a normalized/canonical url?

A: Canonicalization is the process of picking the best url when there are several choices. For example, most people would consider these the same urls:
www.example.com
example.com/
www.example.com/index.html
example.com/home.asp
Note: But each above URL is treated as a different URL.

always use same case & pattern while typing URL in code.