The mapiq or (older) mappiq is a punctuation mark in Hebrew that indicates that a final h is actually pronounced as an aspirate, rather than silent. (At least, in Biblical Hebrew: ariels says it isn't any more in Modern Hebrew.) It's a dot in the middle of the letter ה. It means "extending".

Usually the final ה just indicates that the preceding vowel is long. This is usually a long â, but is sometimes an ê.

One example of the use of mapiq is the feminine possessive suffix -âh, e.g. סוּסהּ sûsâh "her horse". The same letters סוסה would be pronounced sûsâ without it.

The same dot mark inside other letters is called dagesh and has quite a different meaning: it indicates either doubling of the consonant, or plosive pronunciation, depending on the letter and its position. The inside dot is also used inside vav for the vowel-sign shureq, pronounced û. It's called mapiq only with the final H.

The Unicode for all three of mapiq, dagesh and shureq is ּ

R.K. Harrison, Teach Yourself Hebrew, English Universities Press, 1955