To require means to need something necessary or to demand it as mandatory. When your teacher requires you to show your work on math problems, she's saying it's not optional: you must do it. When a recipe requires two cups of flour, that's how much you need for it to work properly.

The word carries a sense of necessity or obligation. A plant requires sunlight and water to survive; these aren't suggestions but actual needs. A job might require certain skills or experience, meaning you can't get hired without them. Schools often have requirements for graduation: specific classes you must take and standards you must meet.

Notice the difference between require and simply want or prefer. Your parents might prefer you to eat vegetables, but they require you to finish your homework before playing video games. That makes it non-negotiable.

When something is required, it's often called a requirement. Meeting these requirements means you've done what was necessary or demanded. Sometimes people use phrases like “the bare minimum requirement,” meaning the absolute least you must do to meet the requirement.