Longman Dictionary of Contemporary English
Wiktionary
n. A public school with specialized courses.
Wikipedia
In the U.S. education system, magnet schools are public schools with specialized courses or curricula. " Magnet" refers to how the schools draw students from across the normal boundaries defined by authorities (usually school boards) as school zones that feed into certain schools.
There are magnet schools at the elementary, middle, and high school levels. In the United States, where education is decentralized, some magnet schools are established by school districts and draw only from the district, while others are set up by state governments and may draw from multiple districts. Other magnet programs are within comprehensive schools, as is the case with several "schools within a school." In large urban areas, several magnet schools with different specializations may be combined into a single "center," such as Skyline High School in Dallas.
Other countries have similar types of schools, such as specialist schools in England. The majority of these are academically selective. Other schools are built around elite-sporting programs or teach agricultural skills such as farming or animal breeding.