I think the simplest explanation is; "An expression can be used where a value is expected". What is sometimes confusing, is that some statements also double as

I think the simplest explanation is; "An expression can be used where a value is expected". What is sometimes confusing, is that some statements also double as expressions, that is, also return values; and that it also depends on the language. eg. the assignment statement returns a value in C and Javascript, but not in Go or Python; printf("%d\n", a = 42); // out: 42 console.log(a = 42) // out: 42 fmt.Printf("%d\n", a = 42) // out: syntax error: unexpected =, expecting comma or ) print("%d" % a = 42) # out: SyntaxError: expression cannot contain assignment, perhaps you meant "=="? Also depending on the language, expressions themselves may be valid statements. For example, this compiles in C; int main() { 12 + 42; } ;this is a valid python program: 12 + 42 ;but if I try this in Go: package main func main() { 42 } // ./main.go:3:5: 12 + 42 (untyped int constant 54) is not used