Hand gestures can have very different meanings across cultures. The speaker provides examples of common gestures and how their meanings vary, such as how a peace sign with the palm facing inward in Australia implies "go screw yourself." It is important to understand the cultural meanings of gestures when traveling internationally to avoid unintended offenses. The document outlines various gestures like thumbs up/down, OK signs, snapping fingers, and more, explaining how their implications differ greatly between regions and can even be considered rude insults. Cross-cultural communication requires awareness of these subtle but important cultural nuances in body language.