Explain density in simple words.

Hint: It is a physical property of the material. A physical property is a characteristic that can be determined without changing the chemical identity of a substance.

Complete answer:
-It is the measure of the mass of an object per unit volume. It is denoted as \['\rho '\].
\[\rho =\frac{M}{V}\]
Where \[\rho \] is the density, \[M\] is the mass in kgs and \[V\] is the volume in \[{{m}^{3}}\]. Therefore, the SI unit of density is \[kg/{{m}^{3}}\]. Density of water in S.I units is \[1000kg/{{m}^{3}}\]. In C.G.S units, the units of density are \[g/c{{m}^{3}}\] and density of water in C.G.S units is \[1g/c{{m}^{3}}\].
-You must have seen that the oil floats on water. It is because the oil has less density than that of water. This means the amount of mass present per unit volume of oil is less than the mass present per unit volume of water. But there is one more reason behind this and that is the two liquids, oil and water are immiscible liquids. It means they do not mix with each other even if we shake them. They separate out into two layers when kept undisturbed for sometime.
-One important feature about density is that it is an intensive property, which means that it is a property that is the same no matter how much of a substance is present.
-So, a litre of water has the same density as that of a single drop of water.

Note:
It is wise to keep in mind that density is dependent on temperature. When the water is heated or cooled, its density changes. With increase in temperature, at constant pressure, density decreases.