Null
Null is a symbol used to indicate the absence of an expression or a result. When it appears as an output expression, no output is printed.
; ; ... ; ; returns Null, and prints no output. Expressions like f[,,] are interpreted to have Null between each pair of adjacent commas.
Further Examples
Null is a symbol used to indicate the absence of an expression or a result. When it appears as an output expression, no output is printed. 
; 
; ... ; 
; returns Null, and prints no output. 
,,
] are interpreted to have Null between each pair of adjacent commas. 
