A mound is usually a formation of dirt or “earth”.
A pile is a formation of just about anything that can be stacked up. Plus it can be hemorrhoids.

A mound has an implied gently rounded shape, a pile can be any shape as long as it goes up in the middle.
A mound connotes a more or less homogeneous, fine-grained consistency.
A pile can be composed of any combination of anything, old appliances, stacks of newspapers, dirt and rubble, dead birds, discarded clothing.
A mound suggests a certain artful effort to shape it, a pile does not even have to be created by human hands.

I would add a mound is more solid, mound of clay. IMO a mound is more permanent than a pile. The pile is just there until it gets moved somewhere else or the contents of the pile get used up eventually.

A pile is dirty laundry…a mound is unfolded clean laundry. Only time I use either word and I can point and say to the kids…“you – pile” and “you – mound” and they know what to do.

I think in general, I think a pile is made up of more clearly discrete objects. Further, I think that it would be awkward to refer to something made up of heterogeneous materials (just take everything out of that room and throw it in a pile in the backyard) as a mound.

Mounds™ don’t have almonds in them, and they’re covered with dark chocolate.

But seriously, a mound is more of a deliberately built and more or less designed feature, say, of a landscape. A pile is just ‘a place where things are accumulated’.

A mound is usually created by man and has a purpose.

A pile can be created by man or animal and has no purpose. example: a pile of dog poop!

A mound is a large, more rounded, pile made of dirt. A pile can be of almost any size, and is made of anything ,as long as it is somewhat stacked up.