A mathlete is a person who competes in mathematics competitions at any level or any age. The term is a portmanteau of the words mathematics and athlete.
Top mathletes in the United States compete on the AIME, USAMO, and ARML. Those in other countries generally participate in national olympiads to qualify for the International Mathematical Olympiad.
Participants in World Math Day are commonly referred to as mathletes.
The Putnam Exam: The William Lowell Putnam Competition is the preeminent undergraduate level mathletic competition in the United States. Administered by the Mathematical Association of America, students compete as individuals and as teams (as chosen by their Institution) for scholarships and team prize money. The exam is administered on the first Saturday in December.
The academic off-season (traditionally referred to as "summer") can be especially difficult on mathletes, though various training regimens have been proposed to keep mathletic ability at its peak. Publications such as the MAA's The American Mathematical Monthly and the AMS's Notices of the American Mathematical Society are widely read to maintain and hone mathematical ability. Some coaches suggest seeking research internships or grants, many of which are funded by the National Science Foundation.