Queen’s Gambit
In any event, the Queen's Gambit and Queens Gambit Declined are both a major opening with lots of theory on both lines.
There are a bunch of other well developed gambits in other openings, but in the 1800's, there were some really deadly gambits that were invented.
For the most part those lines are dead, because high level modern players would never take the bait. But for a long time in chess, it was considered unsportman like to not take a piece that was offered.
I don't recall which grandmaster changed that, in the late 1800's, but he could easily see the deadly trap if he took the piece. It didn't take long for the rest of the chess playing world to follow suit.
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