A Cornish pasty is a large, half-moon pastry enclosing chunks of beef skirt, finely chopped potato, and turnip with lashings of black pepper and a slab or two of butter.
The pastry, which is somewhere between shortcrust, flaky, and hot-water crust, should have the rigidity to withstand being transported, as traditionally they were taken down the tin mines to have as "crib" (Cornish for a mid-morning snack).
The pasty's edge is crimped on the side, never the top, and was traditionally thrown away because the miner's hands would have been covered in arsenic and other metals, which are a tad deadly if ingested.
If you're in the UK, I'm afraid you'll have to go to Cornwall if you'd like to eat a decent pasty.