How does this variable definition work?

Question

C++ / C#

Recently I came across an interesting definition of a variable in the C language:
char c = 2["abcdf"]
To my surprise, the value 'c' was written to the variable c. Could someone explain how this works (not just a guess, I figured out how it happened myself). Namely, to explain what such a definition is called, why it works, where you can read more about such definitions or similar interesting features of the c / c ++ language

Answer 1

address arithmetic.
i[A] == *(A+i) == A[i].