Semantics

side
Он любит спать на левом боку. He likes to sleep on his left side.
hip
На её левом боку болталась сумка. A purse hung on her left hip.
flank
корова с худыми боками a cow with bony flanks
This entry is concerned with the use of the word бок to refer to the lateral part of the body, especially of the trunk, of a human or animal. Common sense will dictate which of the expressions in this entry can or cannot be used to refer to animals or humans. The meaning "(left/right) side of an object," e.g. левый бок лодки "the left/port side of a boat," is not discussed in this dictionary.