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.