Concise answer
Hyperpigmentation is a broad description for darker colour, while melasma is a recurring patterned form often influenced by light, heat, hormones and individual susceptibility.
Post-acne marks, sunspots and irritation-related pigment are also hyperpigmentation but do not behave exactly like melasma.
Distribution, trigger history and skin examination guide the distinction and help avoid overly aggressive treatment.
When evaluation may help
Review is useful for new, changing or recurrent patches and before using strong lightening products, peels or laser procedures.