Let's see if this helps.
Flight attendant jump seats are those padded fold down shelves with seat belt and shoulder harness that flight attendants occupy for take-off and landing. In the U.S., F/As are required to sit on those seats for taxi, take-off, and landing. They may be up and about during taxi to perform a safety related duty -- delivering drinks is not a safety related duty. Many airplanes have more of these seats than the plane usually has flight attendants. For example, the 733/4s have jump seats for four F/As, but the craft is normally staffed with three. As a general rule, a flight attendant who works for that airline can ride on that jump seat if the flight is full. There are rules that go with this as to mode of dress, display of ID
, and certain behaviors. For example, a F/A riding the F/A jump seat may not consume alcoholic beverages. Nor may she ride that jump seat if she has been drinking or is otherwise intoxicated.
The cockpit jump seat is often little better than a fold down shelf right inside the cockpit door. However, the 76s, for example, have two "jump seats." These jump seats are essentially full blown pilot seats. There is good reason for the two. On flights of longer than 8 hours, a flight flown by a U.S. carrier must have, by FAA regulation, a Captain, a First Officer, and an International Relief Officer (IRO). This makes it possible for all three pilots to be in the cockpit and still have an FAA inspector or check airman from the airline giving a check ride. On 76s operating domestically, the 76 operates with 2 pilots and it would be possible to have a pilot riding jump seat and an FAA inspector in the cockpit at the same time giving a check ride.
Sometimes one of the two jump seats seats in the cockpit will be called an "Observer" seat. The other will be called the Jump Seat. This is to differentiate which seat an inspector or check airman would sit in and which one a run of the mill jump seat rider would sit in. Of course, if there is no inspector or other priority jump seat rider, both of the seats could be occupied by off duty pilots. They often are.
TBear, the DC-9s, 727s, and F-100s all have a flight attendant jump seat all the way in the back of the plane. On the 72s, it's attached to that big "vault" door that's back there. On the 9s, it's attached to a door or large hatch. On the F-100s, it's attached to a weight bearing bulkhead (wall). On all of these airplanes it is directly at the end of the aisle, almost between the last rows of seats. On all of these airplanes, it's a double jump seat (designed for two flight attendants). On the F-100s, it's also between the two lavatory doors.
The flight attendant jump seats are not obvious items, and passengers walk right by the retracted jump seats when they board and deplane. In fact, they are so unnoticeable that lots of people think flight attendants stand up for take off and landing. These seats are spring loaded and retract rather rapidly when there is no weight on them. Years ago a slang term for them was "Fanny Slappers" because if you don't move fast enough they slap your fanny when you get up.
The flight attendant jump seats are evenly distributed throughout the cabin depending on the size and model of the airplane.
In the U.S., no one other than designated people may occupy those F/A jump seats. This is normally limited to flight attendants working the flight and a flight attendant riding jump seat on her own time. It is not a free for all where anyone who sees it may sit on it. This is also as per FAA regulation. A flight attendant supervisor giving an observation ride may sit on that jump seat if she is a qualified flight attendant. If she is not, she must occupy a passenger seat.
Those FAA regs have a double enforcement with them: the flight attendant is personally required to enforce them. The airline is required by FAA regs to also require the F/A to enforce them.
I hope this gives some information. Any more questions -- just ask.