"Set Variable" is an Action in the Starcraft 2 Galaxy Editor's Trigger editor, which sets a predefined variable to a value of its type.
Variable - Set Variable = Value
|Variable||Any||Variable (Null)||The variable that a value will be assigned to||Any variable or value of type <Unit>|
|Value||Type of previous argument||Point (Null)||The value that will be assigned to the variable in the previous parameter||Any variable or value of the same type as the previous parameter|
A variable can only be assigned a value that is the same type of the variable. For instance, despite being semi related, you cannot assign an <Integer> to a <Real>, or vice versa. However, numerous conversion functions exist to switch between different variable types.