A guided tour, as the name implies, is led by a tour guide who not only shows you the way but has insights and information to share along the way so you get the most out of your trip.
The opposite is a self-guided tour where you're on your own riding but have maps, cue sheets and/or guiding by GPS. There is usually a full briefing at your accommodation on the first night.
A hosted tour is in between. There is a ride or tour leader, who may or may not be riding with the group. You will be supplied with maps and information about the area and route to give you the local insights.