Alla Bolognese generally means “with ground meat.”
In Italian, a Bolognese sauce is a tomato-based sauce with meat in it. It may be called either “sugo OR ragù (both mean sauce) alla Bolognese.”
Though ground meat is used now, originally it was meat cut by hand into small pieces, then simmered for four hours or more until it started to practically blend into the sauce.
Spaghetti alla Bolognese, or “spag bol” as it’s fondly known in the English-speaking world, isn’t actually an Italian dish. Italians consider spaghetti the wrong shape to hold a meat sauce. You’re more likely to get a Bolognese sauce with tagliatelle in Bologna, or with penne, fettucine or lasagna noodles in a dish of lasagna.
Sometimes, when used in reference to some fish dishes, “Alla Bolognese” doesn’t mean a meat sauce; rather, it can just mean ingredients typically used in Bologna.
For instance, a recipe called “Tortellini alla Bolognese in Brodo”, calls for Prosciutto, Mortadella, and Parmesan, all ingredients from Emilia-Romagna, the “regione” that Bologna is in.
Another, “Braciole di Maiale alla Bolognese”, probably owes its “alla Bolognese” distinction to the prosciutto that it uses to wrap the pork chops in.
Bologna, Italy was a very rich, prosperous area, and so able to afford meat in a sauce.