Requisite means required or necessary for a particular purpose. Something that's requisite is essential: you actually need it to accomplish your goal. A requisite skill for playing basketball is being able to dribble the ball. The requisite equipment for scuba diving includes a mask, fins, and an oxygen tank. Without these requisite items, you simply can't do the activity safely or properly.

Teachers often list the requisite knowledge for a course, the things you need to know before you start. A chemistry class might have a math course as a requisite (sometimes called a prerequisite), meaning you must complete that math class first.

If you're planning a camping trip, requisite supplies might include a tent, sleeping bag, and flashlight. You could leave behind extra pillows or a camp chair, but the requisites are non-negotiable. They're what you absolutely must have to make the trip work.

Notice how requisite sounds formal and serious, matching its meaning: when something is requisite, there's no getting around it.