It is a large, sweet, heart-shaped, red chili pepper. They are commonly used to stuff green olives and to make pimento cheese.
It's a sweet pepper often used as a stuffing for green olives.
Canned (or jarred) roasted red sweet peppers work just fine!
Pimentos trees are native to tropical regions of the West Indies, Central America and South America. For more information on Pimentos http://www.onestopsolver.com/what-is-allspice.html
They use a machine. See the Related Links for more information.