The phrase "Czech mate" is a play on words, combining "Czech" with "checkmate." "Czech" refers to the Czech Republic, a country in Central Europe. "Checkmate" is a term used in chess when a player's king is in a position to be captured (in check) and cannot escape capture on the next move (mate), resulting in the end of the game.
When someone says "Czech mate," it's typically meant as a humorous or punny way of saying "checkmate" while referencing the Czech Republic. The phrase is often used informally in a lighthearted manner or as a joke, especially among chess enthusiasts or those familiar with the game.