The word domino has two main meanings:

1. A small rectangular tile used in a popular game. Each domino is divided in half, with dots (called pips) on each side, ranging from zero to six dots. Players match dominoes end to end by number: a tile with three dots on one end can only connect to another tile's three-dot end. The game requires strategy and a bit of luck, as you draw dominoes from a pile and try to play them all before your opponents do.
2. A chain reaction where one event triggers the next, like dominoes falling in sequence. When you stand dominoes on end in a line and knock over the first one, it hits the next, which hits the next, creating a cascading effect. This idea applies beyond the game: if you forget your homework, you might miss recess to finish it, which means you're tired in your next class, which leads to trouble focusing. Each consequence triggers another, just like falling dominoes. People call this a domino effect. During the Cold War, politicians worried about a “domino theory”: if one country fell to communism, neighboring countries might follow, one after another.