@Darin14 16 is the maximum number of people that Airbnb allows to be registered and paid in a booking. Airbnb introduced this rule in 2020 because of all the bad press they were getting about Corona parties.
Practically speaking, how many people are allowed onto the property is really up to the host and to whatever local laws and HOA rules apply. You can choose any number from 1 to 16 as the maximum number of guests in your settings.