So, a modular propeller is like a toy car that has different parts you can take off and on to make it work better. Instead of a toy car, it's a propeller that goes on a plane or a boat.
On a regular propeller, everything is stuck together and you can't change anything about it. But with a modular propeller, you can take off certain parts, like the blades or the tip, and put on different ones to make it work better for the situation.
It's kind of like building with Legos. You can take some blocks apart and put different ones on to make a bigger or cooler structure. With a modular propeller, you can take parts apart and put different ones on to make it more efficient or better at going through different types of water or air.
By making these changes, you can make the propeller work better and make the vehicle it's on go faster or use less fuel. That's why modular propellers are important in making planes and boats more efficient!