Quantum Entanglement is when two or more particles become connected in such a way that the state of one particle can be instantly affected by the state of the other, even if they're on opposite sides of the universe.
Imagine two friends, Bob and Alice. They're on opposite sides of a mountain, but they're connected by a magical, invisible string. When Bob eats a sandwich, Alice's sandwich also gets eaten, even though she's on the other side of the mountain.
Quantum Entanglement is Weird Superposition Shenanigans