A thought experiment is an extended analogy that includes some element of experimentation.
Not to be confused with thinking about an experiment that has already happened. Some may call any hypothetical or counter-factual thought a thought experiment, but they are not to be confused either.
Overview:
Thought experiments are imaginary scenarios invented with the purpose of exploring all possible outcomes. They are used to envoke thought and investigate the nature of anything. This device is used in all types of academics including the maths, the sciences, philosophy, and literature. Accompanying a thought experiment is usually a diagram to help the reader visualize the experiment. Thought experiments are usually used for three main reasons, "First, we use thought experiments to make arguments; second, we read thought experiments in strongly allegorical terms; and third, the terms of criticism we apply to thought experiments and to works of literature differ"1.
Origin:
In the 1900s, scientist Hans Christian Ørsted coined the term of an experiment that requires no equipment. He called this type of experiment gedankenexperiment, a German word that translates to experiment conducted with the mind2. He only named the term though, not the actual act. Uses of thought experiments trace back to ancient Greece, and Galileo.
Examples of Thought Experiments
1. The Trolley Dilemma
This thought experiment deals with decisions. To put it simply, a trolley is coming down the tracks at a rapid speed. The tracks split into two, on one, you have one person tied down and on the other, you have five people tied down. You are next to a lever that can change which tracks the trolley goes onto. Do you choose the tracks with one person or the other with five people? The outcome can change with more of the variables that are added in but overall, it's an experiment that challenges how you think about the situation.
A way to test this out without having to actually make any real, life-threatening decisions is by playing this game: The Moral Machine.
Rather than a trolley, it deals with self-driving cars, people in those cars, and the people on the crosswalks.
http://moralmachine.mit.edu/