Sometimes even good players get these two words confused.
A gambit usually occurs in the opening. A player would freely give up a pawn in hopes of gaining something in the future. Such things include an open file for a rook, a gain of a tempo (or more), or more spectacular ways, a king hunt or a forced mate.
Many openings contain the word gambit in their name. Examples include the King’s Gambit (1.e4 e5 2.f4), the Queen’s Gambit (1.d4 d5 2.c4), the Albin Counter Gambit (1.d4 d5 2.c4 e5), the Budapest Gambit (1.d4 Nf6 2.c4 e5), From’s Gambit (1.f4 e5 2.fxe5 d6), the Benko Gambit (1.d4 Nf6 2.c4 c5 3.d5 b5), and the Latvian Gambit (1.e4 e5 2.Nf3 f5).
A piece sacrifice usually occurs in the middle game or endgame. In this case, a player freely gives up a piece, instead of a pawn, to gain the same as a gambitted pawn. The type of sacrifice, because of the value of a piece is much greater than a single pawn, is much rarer. It is appropriate to call these sacrifices as attacks if it is part of an opening.
The Fried Liver Attack (1.e4 e5 2.Nf3 Nc6 3.Bc4 Nf6 4.Ng5 d5 5.exd5 Nxd5 6.Nxf7) is a well-known piece sacrifice in the opening. There are others.
That would seem to be easy to remember. But there are some exceptions, although there are (apparent!?) valid reasons for these exceptions.
The first one is the Marshall Attack, which involves Black giving a pawn in the Ruy Lopez. The opening moves are (1.e4 e5 2.Nf3 Nc6 3.Bb5 a6 4.Ba4 Nf6 5.O-O Be7 6.Re1 b5 7.Bb3 O-O 8.c3 d5). So why is this variation of the Ruy Lopez not called a gambit?
It turns out that there is a Marshall Gambit. In fact, there are two of them.
Here is the first Marshall Gambit: 1.e4 d5 2.exd5 Nf6.
And here is the second: 1.d4 d5 2.c4 e6 3.Nc3 c5 4.cxd5 exd5 5.e4.
Even though Frank Marshall was a great American player, having third opening system with “Marshall Gambit” would seem at least a little confusing.
Another opening that may confusing, at least as far as it’s name, is the Muzio Gambit (1.e4 e5 2.f4 exf4 3.Nf3 g5 4.Bc4 g4 5.0-0). Here White is giving up a knight to use the open f-file to attack Black’s king. If a piece is being sacrificed, then shouldn’t it be called the Muzio Sacrifice or the Muzio Attack?
I agree. I haven’t figured out this one yet.
Here is one even more confusing.
The Wilkes-Barre Variation begins with the moves 1.e4 e5 2.Nf3 Nc6 3.Bc4 Nf6 4.Ng5 Bc5. There is no gambit, attack, counter-attack, or sacrifice attached to the name. Maybe it’s because it is unclear who is doing the sacrificing and what is sacrificed. Play over a few games and let me know what you think which word works best. Or create your own.
The Gambit Chess Player 