Distinguish between elasticity of demand and price elasticity of demand. 

Elastic of demand is the measure of the degree of responsiveness of quantity demanded of a commodity to changes in the factors that affect demand.

Or

Elastic of demand is the propionate change in quantity demanded of a commodity to proportionate change in the factors that affect its demand.

Whereas

Price elasticity of demand is the degree of responsiveness of quantity demanded of a commodity to changes in its price.

Or

Price elasticity of demand is the proportionate/percentage change in the quantity demanded of a commodity to proportionate/ percentage change in its price