@PrintDrivr is right — they’re called ink traps.
Well, they’re not real ink traps. They’re trendy affectations pretending to be ink traps. These pseudo ink traps have come about as the result of some typeface designers looking at old printing samples, seeing real ink traps, deciding they’re cool and copying them.
I’ll explain. Head back a hundred or two hundred years ago, and printing was rarely crisp and clear like it is today. After a few uses, the metal type would get grimy with ink. The paper was typically soft and absorbent. The relief printing methods used at the time, such as letterpress, were rather crude by today’s standards.
Anyway, between the absorbent paper, the metal letters pressed against the paper, and the sticky ink spreading, the printing would lose its sharpness. The spots particularly prone to blurring and filling in were the tight spaces where two strokes came together at acute angles. To help mitigate the problem of these spaces gumming up with ink, the metal type designers would cut tiny grooves into the sharp corners. These small notches were known as ink traps because they provided a little extra space for the ink to accumulate. The result was the ink filling in these little gaps, which allowed the sharp angles to remain mostly sharp when printed.
Today, there’s little practical need for ink traps, but some type designers have engaged in a fad of including them in their type designs — not to trap the ink, but because they think they’re cool, in sort of a hipsterish kind of way. If you haven’t guessed, I think the fad is a bit stupid.