The void type, in several programming languages derived from C and Algol68, is the return type of a function that returns normally, but does not provide a result value to its caller. Usually such functions are called for their side effects, such as performing some task or writing to their output parameters. The usage of the void type in such context is comparable to procedures in Pascal and syntactic constructs which define subroutines in Visual Basic. It is also similar to the unit type used in functional programming languages and type theory. See Unit type#In programming languages for a comparison.
C and C++ also support the pointer to void type (specified as void *), but this is an unrelated notion. Variables of this type are pointers to data of an unspecified type, so in this context (but not the others) void * acts roughly like a universal or top type. A program can convert a pointer to any type of data (except a function pointer) to a pointer to void and back to the original type without losing information, which makes these pointers useful for polymorphic functions. The C language standard does not guarantee that the different pointer types have the same size or alignment.