A weigh-in is the official weighing of a competitor before a contest, done to prove they are inside the weight limit for their class. It is a fixed event, not just an action: in boxing, wrestling, judo, taekwondo and MMA it happens the day before or the morning of the fight, in front of officials, usually with cameras and often with the two fighters standing face to face afterwards. In horse racing, the jockey is weighed with the saddle — there the weigh-in makes sure each horse carries a fair load. Because of the drama around it, the word carries more than measurement: fighters starve and dehydrate themselves to "make weight," and a fighter who is over the limit at the weigh-in can lose the bout before it begins. English also uses `weigh-in` loosely for any formal weighing where the number matters and people are watching — at a gym programme, a diet club, or a school sports day. Write it with a hyphen when it is the noun; the plural is weigh-ins. It comes from the two-word verb `weigh in`, which still lives on its own with a related meaning and a quite different one: `weigh in` can mean to be weighed before a contest ("he weighed in at 72 kilos"), and it also means to join a discussion with your opinion, often forcefully — "the boss weighed in with a few complaints." That second sense is the one you will hear most often in ordinary news and office English.