A land mine (sometimes just called a "mine") is a weapon that is put on the ground or just underneath the ground so that it explodes when a person or vehicle goes by. They are called "mines" because people who put them there dig a hole in the ground (like miners who dig for coal etc.). Many people can be killed by mines, including innocent people. Sometimes mines can lie in the ground for years after a war has ended and people get killed or badly injured.
There are different types of land mines. Anti-vehicle mines are against vehicles. Infantry mines are used against foot soldiers.