Terma is a special type of sacred teachings in some religions, especially in Tibetan Buddhism. Imagine if you had a secret box that you hid in a very special place. This box had something very important inside it, like a treasure map or an important letter. You didn't tell anyone where the box was or what was inside it, but you left a special clue or map so that someone could find it in the future when the time was right.
That's kind of what terma is like. A long time ago, a very wise and special person in the religion hid some special teachings or rituals in a secret way. They did this because they believed that the world wasn't ready for these teachings yet, but that in the future, when the time was right, someone would discover them and share them with others.
So, terma is like finding a secret treasure or message from the past that has been hidden away until the time was right to share it. It's a really special and secret thing in some religions, and people who find terma are considered to be very lucky and blessed.