Great question! So, when you purchase a CD/share certificate, you invest a set sum of money for a fixed period of time (we call this a "term"). Terms can be six months, one year, 18 months, or more.
In exchange for your pinky promise (well, your signature. Can't run a business on pinky promises.) we pay you interest at regular intervals or at the end of the certificate’s term (we call this "maturity" or "coming due"). At maturity, when you cash in or redeem your certificate, you receive the money you originally invested plus any accrued interest.
Sound too good to be true? Well, here's the catch. You have to wait until the end of the term or if you redeem your certificate before it matures, you may have to pay an early withdrawal penalty or forfeit a portion of the interest you earned.
Good things come to those who wait, after all.