The short answer
Msemen is a square, layered flatbread, folded and griddled until flaky, then brushed with butter or oil. Baghrir is a soft semolina pancake cooked on one side only, so the top sets into hundreds of tiny holes. Both are breakfast breads eaten with honey and mint tea, and both turn up on the Ramadan table.
In more detail
Msemen is about layers. The dough is stretched thin, folded over on itself into a square and cooked on a hot griddle, so it comes out flaky and slightly chewy. Locals tear it by hand and dip it in honey or melted butter, often standing at a counter or on a plastic stool before work.
Baghrir is about holes. It is a batter of semolina poured onto the griddle and cooked on one side only. As it cooks, bubbles rise and set, leaving a spongy top covered in tiny holes. It is soaked in warm butter and honey, which runs into every hole. Sticky by design: a napkin is fine, and licking your fingers is not frowned on.
You find both at the dawn breakfast counters in most neighbourhoods from about 06:00, with the counters near Bab Doukkala among the best known. Look for a woman folding dough beside a hot griddle. Baghrir is also on most riad breakfast tables, and Bakchich Cafe off Jemaa el-Fnaa serves msemen with honey and butter.
If you want to make them yourself, bread and msemen workshops are among the cooking classes on offer in Marrakech.