What is the name of the dot over "j" and "i"?

This is something I've wondered about from time to time. It turns out that

The small distinguishing mark you see over a lowercase /i/ and a lowercase /j/ is called a tittle - an interesting name that seems like a portmanteau (combination) of "tiny" and "little," and refers to a small point or stroke in writing and printing. Generally, a diacritic dot such as a tittle is also referred to as a glyph. However, in regards to /i/ and /j/ - the removal of the mark is still likely to be read as /I/ or /J/; as such, these are not examples of a glyph.

Derived from the Latin word "titulus," meaning "inscription, heading," the tittle initially appeared in Latin manuscripts beginning in the 11th century as a way of individualizing the neighboring letters /i/ and /j/ in the thicket of handwriting. With the introduction of the Roman-style typeface in the late 1400's, the original large mark was reduced to the small dot we use today.

More details here.