About

The case of a letter refers to its representation.

The most known cases are:

• upper case (ie UPPERCASE, LOWERCASE)
• and lower case (ie lowercase, uppercase)

but there is more:

• Camel Case: UserCount used in java code for instance
• Snake Case: user_count used in properties for instance
• SQL Case: USER_COUNT used in SQL (known also as SCREAMING_SNAKE_CASE or UPPER_SNAKE_CASE)
• Hyphen Case: user-count also known as kebab-case, lisp-case, etc.

Historically

They refer to the physical cases where printers kept their letters

Where you can see a physical representation of letter frequency.