A data definition statement sets aside storage in memory for a variable and may assign a name to the variable. Each data definition has the syntax:
[ name ] directive initializer [, initializer ] ...
Name
A variable name is a label that marks the offset of a variable from the beginning of its enclosing segment. For example, suppose that was located at offset 0 in the data segment and consumed 2 bytes of storage. Then would be located at offset 2.
Labels are identifiers that act as a place marker for data/instructions.
Identifiers are programmer-chosen names.
Some examples are: , , , , or .
Rules for creating them are
They may contain between 1 and 247 characters.
They are NOT case-sensitive.
The first character must be either a letter (A..Z, a..z), _, @, ?, or $. Subsequent characters may also be digits.
An identifier can not be the same as a reserved word.
Reserved words have special meaning and can only be used in their correct context. They can be any of the following:
Instruction mnemonics, such as , , or
Directives, such as or
Attributes, such as or
Operators, such as +, or –
Predefined symbols, such as
A list of the MASM reserved words can be found from here.