Counter
The inside of a bowl.
Leg
The bottom stroke of a letter, such as the base of an "L" or diagonal stroke of a "K."
Shoulder
The curve at the beginning of a leg of a character, such as in an "m."
Sources:
"The Little Know-It All: Common Sense for Designers." Die Gestalten Verlag GmbH & Co. KG (dgv), Berlin 2007.
Gavin Ambrose, Paul Harris. "The Fundamentals of Typography." AVA Publishing SA. 2006.