Kalmar "hadal" sifa ce da ke nufin zurfin zurfin teku, yawanci ƙasa da mita 6,000 (ƙafa 19,700). Ana amfani da shi sau da yawa don kwatanta yankin hadal, wanda shine yanki na teku wanda ya tashi daga kusan mita 6,000 zuwa kasan ramukan teku, wanda zai iya kaiwa zurfin fiye da mita 10,000 (ƙafa 32,800). Kalmar "hadal" ta fito daga kalmar Helenanci "Hades," wanda shine sunan allahn duniya a cikin tarihin Girkanci.