How to define a countergambit? Am wondering if there is a definition of a countergambit. My understanding is, a countergambit happens when one side plays a gambit, instead of capturing the pawn, the other side also sacrifices a pawn.

Is my description accurate? Is the following line considered as a counter gambit?


f4 e5 2. e4


The move e5 is called From's gambit. Instead of capturing the pawn, white develops his king pawn, offering his f4 pawn. Is this considered as a countergambit? (Under a different move order 1. e4 e5 2. f4 it is called king's gambit.)
You're right: a counter-gambit is an opening in which one side plays a gambit, and the other side rejects the gambit with another gambit (i.e. "gambits" the gambit). A popular counter-gambit is the Albin Countergambit:

[FEN "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1"]

1. d4 d5 2. c4 e5



  Under a different move order 1.e4 e5 2.f4 it is called King's gambit.


This is also a King's gambit but due to the order it is also cosidered a countergambit

[FEN "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1"]

1. f4 e5 2. e4