What does pure substance mean

An element is a pure substance that cannot be separated into simpler substances by chemical or physical means ... Pure substances are often called pure to set them apart from mixtures. A substance can be anything. It doesn't have to consist of a single element or type of molecule. Pure hydrogen is a pure substance.

Pure substances are defined as substances that are made of only one type of atom or only one type of molecule (a group of atoms bonded together).