When you're defining a programming language, you've got some basic components that make up the language. You've got functions. You've got operators like + and -. And you've got language constructs, which are the keywords that form the heart of the language and which are used to build other features.
Language constructs are built into the language runtime, and execute incredibly fast.
A programming language probably has iteration constructs (for, while), comparison constructs (if, switch), and other features like "require", "include", "print", or "echo".