Mathematics is the long word for "math," or the science of numbers and shapes and what they mean. Most people need mathematics everyday to count and measure.
Mathematics is technically a plural noun — mathematics include geometry, algebra, and calculus. But in the U.S., the word is usually treated as a singular concept: That's why someone says that mathematics is their favorite subject, not mathematics are their favorite subjects. The word mathematics comes from the Greek word manthanein, meaning "to learn."