I would assume that means the next Monday coming up.
My grandmother would always say "Monday week" or "Monday coming" to differentiate but have not heard anyone use those recently.
22nd. In my mind a new week starts on Monday. Use next in reference to a day in a new week. Use this in reference to a day in the current week. Anyone who uses next Monday to refer to a day 10 days into the future molests collies
next monday should only be used if it is currently monday and you are referring to the day 7 days away. If it is tues-sunday monday is the proper word usage.