The term "body clock" refers to the internal mechanism that regulates our sleep-wake cycle. There are a number of synonyms that can be used to describe this aspect of our anatomy, including circadian rhythm, biological clock, natural clock, and internal clock. Each of these terms emphasizes the natural, biological nature of our sleep patterns, and highlights the fact that our bodies are attuned to the rhythms of the natural world. Whether we use the term "body clock" itself or one of these related synonyms, the important thing is to recognize and respect the vital role that our internal rhythms play in regulating our physical and mental health.