The expression "down to the wire" means the outcome of something is not decided until the very last moment. An example of this idiomatic expression in a sentence would be: "The basketball game was very exciting because it went down to the wire." This means one team did not have a distinct advantage over the other team during play. The game was so close the viewers could not tell who was going to win until the last second.
This English saying is often used to describe something that did not happen until the very last moment, as in a newspaper article not being written until right before the deadline. In the case of a college report, a student might say, "I didn't finish my report until five minutes before class started. I really went down to the wire with this one."
It would appear the idiom has its origins in horse racing. A long piece of tape or paper would be placed across the finish line at race tracks. This was used so it would be easier to determine the winner of a close horse race. The horse that came in first would touch the tape or paper first, and it would wrap around the front of the winning horse. If two or more horses were neck and neck until the finish line, the winner often couldn't be determined until one of them touched the wire, hence the race would go down to the wire.
Generally, this term is used to describe a situation that is full of suspense, and is commonly used in English-speaking countries by many sports commentators to describe various sporting events. In July 1889, Scribner's Magazine printed one of the earliest uses of this phrase. While describing a very close horse race and how the horses Timarch and Petrel were head and head, with the two horses racing down to the wire, all the while being cheered on by spectators' applause. Since then, the expression has become a common English idiom.