Why is it interesting?
Layman
Explanations in this section should contain no formulas, but instead colloquial things like you would hear them during a coffee break or at a cocktail party.
Student
A great description can be found at page 257 in "Quantum Field Theory - A Modern Perspective" by V. P. Nair
Researcher
The motto in this section is: the higher the level of abstraction, the better.
Examples
History