A backlight unit is provided that may include a plurality of optical assemblies arranged in a matrix form, and a cover to receive the optical assemblies. Each optical assembly may separately include: a light emitting module having a plurality of light emitting devices, a light guide plate, and a cover provided over a portion of the light guide plate. The optical assemblies may include a first optical assembly, a second optical assembly and a third optical assembly. A top surface of the second optical assembly may be spaced from a top surface of the first optical assembly in a first direction by a first interval, and a top surface of the third optical assembly may be spaced from the top surface of the first optical assembly in the second direction by a second interval.