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 civilians. Sometimes mines can lie in the ground for years after a war has ended and people get killed or badly injured. But can defuse due to age.
There are different types of land mines. Anti-vehicle mines are against vehicles. Infantry mines are used against foot soldiers.