Its just ground(minced)meat mixed with other ingredients like bread crumbs,onion,flavouring. Put into a loaf tin and cooked in the oven. When you turn it out it is the shape of a loaf and you slice it in the same way.
This American has awful memories of awful meatloaf. Mom used huge hunks of day-old bread and ketchup to help hold things together. **Ugh** The few times I've made it, I use rolled oats instead of breadcrumbs and tomato paste instead of ketchup. Small but vital differences.
Just read the recipe warpig cited. Would recommend scrapping the celery and using ground turkey instead of pork (may as well leave one artery unclogged). Better yet, skip this dish entirely.