Statement

A statement is a unit of code that represents an instruction or an action for the computer to perform. For example, in GDScript, a line defining a variable or a function is a statement. A line that creates an if block is a statement, and so is a line that calls a function.

It's different from expressions, which are units of code that output a value. A statement is a more generic concept.

In the GDScript code below, each line is a statement:

var health := 100
func heal():
    health += 10
    if health > 100:
        health = 100

So, when you read something like "an if statement" or "a return statement", the author is talking about a specific type of instruction or action. Respectively, if condition: and return in the example above.