A backlight unit comprising: a housing including a plurality of first fixing parts protruding from the housing and a plurality of second fixing parts protruding from the housing ; a plurality of light source devices ; and at least one optical sheet disposed above the plurality of light source devices , the at least one optical sheet including: - a plurality of upper holes at an upper side of the at least one optical sheet and coupled to the plurality of first fixing parts , - a plurality of lower holes at a lower side of the at least one optical sheet and coupled to the plurality of second fixing parts , and a lateral side forming a first corner with the upper side and a second corner with the lower side of the at least one optical sheet , wherein the plurality of upper holes includes at least a first hole having a first distance to the first corner along the upper side , and a second hole having a second distance to the first corner along the upper side , wherein the first distance is smaller than the second distance, wherein the plurality of lower holes includes at least a first hole having a third distance to the second corner along the lower side , and a second hole having a fourth distance to the second corner along the lower side , wherein the third distance is smaller than the fourth distance, and wherein a size of the second hole of the plurality of upper holes is smaller than a size of the first hole of the plurality of upper holes , characterized in that the first distance differs from the third distance, and the second distance differs from the fourth distance. a housing including a plurality of first fixing parts protruding from the housing and a plurality of second fixing parts protruding from the housing ; a plurality of light source devices ; and at least one optical sheet disposed above the plurality of light source devices , the at least one optical sheet including: - a plurality of upper holes at an upper side of the at least one optical sheet and coupled to the plurality of first fixing parts , - a plurality of lower holes at a lower side of the at least one optical sheet and coupled to the plurality of second fixing parts , and a lateral side forming a first corner with the upper side and a second corner with the lower side of the at least one optical sheet , - a plurality of upper holes at an upper side of the at least one optical sheet and coupled to the plurality of first fixing parts , - a plurality of lower holes at a lower side of the at least one optical sheet and coupled to the plurality of second fixing parts , and wherein the plurality of upper holes includes at least a first hole having a first distance to the first corner along the upper side , and a second hole having a second distance to the first corner along the upper side , wherein the first distance is smaller than the second distance, wherein the plurality of lower holes includes at least a first hole having a third distance to the second corner along the lower side , and a second hole having a fourth distance to the second corner along the lower side , wherein the third distance is smaller than the fourth distance, and wherein a size of the second hole of the plurality of upper holes is smaller than a size of the first hole of the plurality of upper holes , characterized in that the first distance differs from the third distance, and the second distance differs from the fourth distance. <EOS>