Definition of Quality:
Quality of a product/service means 'the fitness for use' of a product.Fitness for use means, it should satisfy all the explicit and implicit requirements of the customer and result in customer satisfaction.
Consider the case of a toy car made for the children.
Explicit requirement: It should function like a car and move smoothly when rolled on the ground.
Implicit Requirement: It should not have sharp edges which can injure the children and the paints should be lead free.