Initialized variable

Initialized variable - is a variable that already has value (or had it before).

Brand new (newly created) variable is "empty" - it has no value - it is not initialized. For that reason some of commands and other functions can not be applied to such variable.

For example you can not forcibly add values to multiple users with un-initialized variables.

Numeric variable that is not initialized will be showing 0 (zero) in macros and expressions.
Date and Time variable that is not initialized will show current bot's system date and time same as it is in dt_now() function - without bot's Time Zone taken in consideration.
Text and Global variables if they are not initialized will not show anything.

Initialized variable can become UN-initialized again. More info in Variables manual, chapter: "Managing by commands".