Protist
Protist is a tiny living thing, often just one cell, that lives in wet places like ponds.
Think of it this way
A drop of pond water on a glass slide holds dozens of tiny living things. Each one moves, eats, and splits in two on its own — just one cell doing all the work. Most are smaller than a grain of flour and thrive wherever water collects.
Explaining protist by grade level
If you look at pond water with a strong lens, you see tiny things that move. Some are round and drift with the flow. Some have thin tails and swim fast. These are not plants or bugs. They are their own kind of life.