Complex sentence: A pork pie hat or porkpie hat is a type of hat made of felt or, less commonly, straw, and similar to a Trilby or a fedora but with a flat top.
Split into simpler sentences: A pork pie hat or porkpie hat is a type of hat made of felt or, less commonly, straw. It is somewhat similar to a Trilby or a fedora, but with a flat top.