Lophodont is a pattern of tooth structure in which an elongated ridge grows between two cusps. (Loph means ridge, and -dont refers to teeth.) This is a very common molar pattern, and can be found in primates, rodents, and elephants, to name a few.
These lophs may be oriented antero-posteriorally (front to back), or labial-lingual (side-to-side). In elephants and some rodents the labial-lingual orientation is carried to an extreme, with the lophs tightly packed until the tooth looks like a washboard. This specific form is called loxodont. This form is well adapted to grinding food.
Primates have a simpler pattern, having only two lophs running parallel antero-posteriorally, a form called bilophodont. (Apes have a modification of this called the Y-5 Molar). These forms are good for crushing and tearing plant matter.
Many animals have a molar pattern in which a single cusp is elongated. This is not considered a type of lophodont, instead falling into a separate category, the selenodont form.