General definition :
Cement is a binder or it can be called as a mineral powder which forms paste or mortar when mixed with gravel/sand along with water and hardens.
Technical definition :
Cement is a mixture of lime (in the form of calcium carbonates), silica and oxides of iron and alumina which are partially fused at a temperature of 1450 deg celcius resulting formation of a grey colour pebble material called clinker which contains tricalcium silicates, dicalcium silicates, tricalcium aluminates and tetra calcium alumino ferrites. The resulting clinker is grinded with gypsum to form cement.
Clinker image
Gypsum image
