A requirement is something that must be done or must be present for a particular purpose. Requirements are the essential conditions that have to be met before something else can happen.

Schools have requirements for graduation: you must complete certain classes, earn a minimum number of credits, and pass specific tests. These aren't suggestions; they're requirements. If you want to join the basketball team, the coach might have requirements like attending all practices and maintaining good grades. A recipe has requirements too: you can't make chocolate chip cookies without flour, sugar, and chocolate chips.

Requirements show up everywhere in life. A library card application might have age requirements. A video game might have system requirements that tell you what kind of computer you need to run it. When scientists conduct experiments, they follow strict requirements to ensure accurate results.

The word emphasizes necessity. Unlike a recommendation (which is optional) or a preference (which is just what someone likes best), a requirement is non-negotiable. When your teacher says reading three books is a requirement for the semester, that means you must read them, not that it would be nice if you did.

People also use required as an adjective, as in “Math is a required subject” or “Helmets are required for bike riders in this park.”