A HAM radio term. A mag mount (mag-mount, magmount) antenna is basically an antenna with a nice,
strong magnet on the bottom, so that it can be affixed to a car (usually on the roof,
unless you are one of those nonconformist types).
These antennas usually go for about
$70 US at a Radio Shack, for a single band antenna. Or, you can go to a
hamfest, and probably get a better price-- I got one for $30. Most often, they come with a PL-259 connector, however, most handheld radios have either BNC or SMA connectors, so you may want to get an adapter. These go for 2-3 dollars US. With mobile radios, it varies.