~~you might know what "monotonic" means if you had googled it, which would also give you the answer to your question~~

edit: this was far too harsh of a reply in retrospect, apologies. the question is answered below, but i'll echo it: a "monotonic UUID" is one that numerically increases as new UUIDs are generated. this has an advantage when writing new UUIDs to indexed database columns, since most database index structures are more efficient when inserting at the end than at a random point (non-monotonic UUID's).