A seal can be either the cute mammal at the aquarium balancing a beach ball on its nose, or the fancy stamp on your diploma that acts as an official "seal of approval" from your school.
Seal is a tricky word since its meanings are so diverse. One type of seal lives in water, coming ashore to breed, give birth, and nurse their young. The largest type of seal — the elephant seal — can weigh 6,000 pounds! On the other hand, seal can also mean a stamp that may be placed on a document to show that the document is official and authentic. And, if you want to make sure that your document is safe in its envelope, you might need to seal (make tight) the envelope with some tape.