Maximum guests is the maximum number of people that a place or bedroom you are looking at can host.
You can find this information right below the place's photo in every listing, or under "Extra per guest" in the Rental Conditions section.
Sometimes the landlord may charge an extra amount per guest. If this is the case, the information will also be shown in the listing.
Always make sure to send a booking request with the exact number of people who will be moving in. Even if the landlords allows a higher number of tenants/guests than what you requested, they will only allow the number of people you added when you sent your booking request. After your booking is accepted and confirmed, it's not possible to change the number of the guests.