Macule
A macule is a flat area of skin that differs in colour from the skin around it, without being raised or depressed. Running a finger over one detects nothing: the change is in colour alone, which is what distinguishes it from a papule.
Flat, and differing only in colour. That is the whole of it, and the precision is the point.
A macule can be darker or lighter than the surrounding skin, and either counts. What it cannot be is raised or depressed: if a finger passed over it detects anything, the word no longer applies.
That distinction is among the first a clinician makes, and it is one anybody can make at home without any vocabulary at all. Closing your eyes and running a fingertip across an area answers it more reliably than looking does, because the eye is easily misled by colour into perceiving relief that is not there.
Size separates a macule from a patch, which describes the same flat change over a larger area. Where exactly the line falls is a matter of convention rather than a hard rule.
The term appears wherever colour changes without texture changing. Areas of pigmentation and areas where pigment has been lost are both described this way, which is why it recurs on pages about melasma and about vitiligo despite those conditions having nothing else in common.
Like every word in this part of the vocabulary, it describes appearance and implies nothing about cause or seriousness.
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