Semantics

knee
Колени у него дрожали. His knees shook.
lap
Он положил голову ей на колени и заплакал. He lay his head in her lap and wept.
This entry is concerned with the use of the word колено to refer to human knees. This word does not refer to animals. In its plural form колени this word is also used to refer to the front part of the human body (from the waist to the knees) when in sitting position ("lap"). This usage is also described in this entry. The word колено is also used to refer to the part of the clothing that covers the knee, e.g. Ну и брюки у тебя! Колени протёрлись. "Look at your pants! Worn through at the knees." This meaning, and also the meaning "bend (of a pipe, river, etc.)," e.g. колено водосточной трубы "elbow (of a water pipe)," and the meaning "generation," e.g. брат во втором колене "first cousin twice removed," are not described in this dictionary.