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In an episode of "Air Crash Investigation" the term "pickle switch" was used. I tried to search this term in all the resources available to me and I didn't find any citation, except in some rare cases regarding military aviation.
In any case, it looks like a not standardized term, and I'd like to know if it really exists (and is thus not fictional), why it is named like this, and is it some kind of slang?
The term pickle switch is now generically used for a kind of handheld electronic switch. They were originally used as the bomb release switch in WWII.
The handle of the switch is a cylindrical object sized to fit in your hand making a fist. It is sometimes ribbed and generally looks like a dill pickle. There is a momentary electric switch on the end that you depress with your thumb.
Here is a photo of a Lancaster bombardier holding a pickle switch. this one does not actually look like a pickle -- I haven't been able to find a photo of one that does. However, it illustrates the use of the handheld bomb release switch.
Here is an illustration of the bombardier control panel from a US bomber training document. The pickle switch is stowed on the side of the panel.
In an aircraft, switches mounted rigidly to the airframe can be a challenge because as the aircraft maneuvers, hits turbulence, gets shot, and generally shakes around it is difficult to reach a particular switch. Furthermore, when the bombardier was heads-down focused on the bomb sight, they needed a bomb release switch they could reliably press with split-second accuracy without diverting attention from the bomb sight. A handheld switch fits the bill perfectly as the operator knows where it is without having to search for it -- and it is depressed with a simple press of the thumb.
Other applications where an operator needs to be able to press a switch without diverting attention to the switch have come to use pickle switches. On modern military aircraft, thumb operated switches on the control stick are likely called pickle switches.
I was watching Jeopardy tonight and recognized that the signaling device they use would be considered a pickle switch.
In the US, the push-to-talk assembly that air traffic controllers hold in their hand is called the "pickle switch." It is indeed about the size of a small pickle, although it is not cylindrical nor is it ribbed. But in keeping with Rob McDonald's answer, it can be held in a closed hand. Some people have it clipped to their belt, their pocket, or their lanyard, however.
It normally means a switch used to "pickle", or jettison, or release, some sort of load or stores, like bombs or drop tanks (it started as a slang term used by bombardiers).
In the civilian world, you most commonly see pickle switches on helicopters with sling load hooks underneath, for releasing the load when dropping it off, or in flight if an emergency comes up. Usually a button, or add-on guarded toggle switch, on the control stick, operated by one of the lower fingers.
When flying with a sling load, you need the ability to pickle the load immediately if it starts to oscillate and jeopardize control of the machine. It's pretty unusual to see a pickle switch on a civilian fixed wing airplane, unless it's equipped to drop stores, like a firefighting airplane.
In Boeing aircraft, the pickle switches are the up/down switches on the yoke that operate the trim motor. The official Boeing name is "Stabilizer Trim Switches". "Pickle switch" is the colloquial name. There are two and both have to be moved at the same time in the same direction in order to make the stab trim move. They are spring loaded to the center (off) position. These are the switches referred to in the Air Crash Investigation series.
This term may also apply to other aircraft.
Anecdote: the yoke mounted stab trim switches on the earlier Boeings operated the trim motor at the highest speed regardless of the speed and configuration of the airplane. There were pedestal mounted switches to operate the trim motor at the lower speed which was desirable in the cruise at high aircraft speeds to avoid abrupt pitch changes. The use of the "pickle switch" during the cruise was frowned upon for this reason and was indicative of an inexperienced or ham fisted pilot.
One prominent accident in which "pickle switches" play a part is Alaska Airlines Flight 261. In this case, the "pickle switches" are the switches on the yoke that are used to set the longitudinal trim - officially, the "Control Wheel Trim Switches". See the official report, page 4, footnote 18.
To answer your question, in this case, in civilian aircraft, "pickle switch/button" is absolutely slang and in no way official and as others have already answered, in this case its referring to the pitch trim on the yoke.
I've been flying since 1974, USAF fighters, civilian biz jets and everything in-between and I've never heard it used in reference to the pitch trim, just the ordinance release button ( on the control stick in my case ) of a military fighter/bomber.
Incidentally, in the case of a "runway" trim as happened in the aforementioned https://en.wikipedia.org/wiki/Alaska_Airlines_Flight_261 incident, you can override a runaway pitch trim with the trim switch to bring it back into trim then pull the circuit breaker to stop it there so it won't go "runaway" again, then, in many, if not all airliners, you have a manual pitch trim wheel in the cockpit to make further adjustments or just manually hold appropriate control pressures from there on. Much better than leaving it in a full deflection position with 120 lbs of pressure required to overcome it.
