A charter flight is made by a person or persons to go where (and when) they want to go.
Much more expensive of course.
A scheduled flight is open to the public, it is a flight that has a planned departure time and destination.
From Wikipedia's comes this explanation:
A charter airline is one that operates charter flights, that is flights that take place outside normal schedules, by a hiring arrangement with a particular customer.
In the context of mass tourism, charter flights have acquired the more specific meaning of a flight whose sole function is to transport holidaymakers to tourist destinations.
Such charter flights are contrasted with scheduled flights, but they do in fact operate to regular, published schedules.
However, tickets are not sold directly by the charter airline to the passengers, but by holiday companies who have chartered the flight (sometimes in a consortium with other companies).
Further information on charter fights at:
http://en.wikipedia.org/wiki/Charter_flights