The name of a variable can contain only Latin Characters (English uppercase or lowercase characters), numbers, and the underscore character ( _ ).
Variable names are case sensitive, which means there is a distinct diefference between uppercase and lowercase characters. Any change in case will completely change which variable you access. For example myVAR, myvar, MYVAR, MyVaR would all be complete different variables.
No space characters are allowed. If a variable is described by more than one word you can use the underscore character ( _ ) between the words. For example the variable name student age is wrong. Instead, you might use student_age, or even studentAge.
A valid variable name can start with a letter, or an underscore. Numbers are allowed, but they cannot be used at the beginning of a variable name. For example the variable name 1student_name is not properly written. Instead you might use student_name1 or student1_name.
A variable name is usually chosen in a way that describes the meaning and the role of its contained data. For example a variable that holds a temperature value might be named temperature, temp, or even t.

Variables