To certify means to officially confirm that something is true, meets certain standards, or is authentic. When a doctor certifies that you're healthy enough to play sports, she's formally stating that you meet the medical requirements. When a building inspector certifies that a new school is safe, he's officially declaring it ready for students.

The word comes from making something certain through official authority. A lifeguard must pass tests before an instructor will certify them as qualified to save swimmers. A jeweler might certify that a diamond is genuine. Organizations certify that organic farmers follow proper growing methods.

When you send an important document by certified mail, the post office provides official proof of delivery. A certificate is the document that proves certification: your birth certificate certifies when and where you were born, while a gift certificate shows that a store owes you a certain amount of credit.

Certification matters because it gives people confidence. Parents trust certified teachers to educate their children. Passengers trust that certified pilots know how to fly safely. Without certification, anyone could claim they're qualified to do important work, whether they actually are or not. Certification transforms someone's claim of “I can do this” into an official “Yes, they really can.”