Case Sensitive means that the case of a letter matters: there is a difference between the lowercase version of a letter and the uppercase version of the same letter.
The following items are usually not case sensitive:
- Top level domains (TLDs)
- User names
The following items usually are case sensitivie:
- Directories and file names
- Web server directories (i.e., folders) and web pages names
Passwords are usually case-sensitive, so "password", "Password", "PassWord", and "passWord" would all be considered different passwords.
Top level domains are not case-sensitive, so "www.example.com", "WWW.EXAMPLE.COM", and "www.Example.com" would all point to the same website.
However, web site directories and web page names are case sensitive:
- "www.example.com/blog/" and "www.example.com/Blog/" point to different directories.
- "www.example.com/welcome.html" and "www.example.com/Welcome.html" are different web pages
Because of this, many content management systems automatically default all directories and web files to lowercase.