What is meant by class legislation?

As per Black’s Law Dictionary, ‘Class legislation’ is term applied to statutory enactments which divide the people or subjects of legislation into classes, with reference either to the grant of privileges or the imposition of burdens, upon an arbitrary, unjust, or invidious principle of division, or which, though the principle of division may be sound and justifiable, make arbitrary discrimination between those persons or things coming within the same class.