Your thighs are the top parts of your legs, between your knees and your hips.
e.g. The pain originated from a point in Maria’s left thigh.
Your knee is the joint between the top and bottom parts of your leg where it bends in the middle.
e.g. Charles went down on one knee and asked her to marry him.
e.g. Barbara was on her knees scrubbing the floor.
e.g. The knee injury forced her to give up running.
Your ankle is the joint where your foot joins your leg.
e.g. He fell and twisted his ankle badly.
Your shins are the front parts of your legs between your knees and your ankles.
e.g. Deborah has a nasty bruise on her shin.
calf /kæf/ (plural calves)
Your calf is the thick part at the back of your leg, between your ankle and your knee.
e.g. He’s torn a calf muscle.