I have no doubt whatsoever that I am about to incur the wrath of other posters but, in the UK, a loaf is a very different product from a muffin.
A "muffin" is approximately 3 inches in diameter, 1/2 to 1 inch deep and made using muffin rings. Traditionally, it is split in half on the horizontal, toasted and buttered and served at tea-time or used for something like "Eggs Benedict". It is a yeasted dough.
A "loaf" is also a yeasted dough (may indeed be a very similar mixture/recipe to a muffin) which can be freeform like a plaited loaf or the dough may be placed in 1 pound or 2 pound "loaf" tins, sliced vertically and used for toast, sandwiches, melba toast, Welsh Rarebit, Bread and Butter Pudding, etc.
All the best,