The most common term for dead leaves that have fallen from trees is simply "leaves" or "fallen leaves".

However, other terms you might use include:

* Leaf litter: This term is often used in scientific contexts or when referring to the layer of dead leaves on the forest floor.

* Dry leaves: This term emphasizes the state of the leaves.

* Autumn leaves: This term is used when referring specifically to leaves that fall in the autumn.

The best term to use will depend on the context of your conversation.