The term "the backs" generally refers to the rear portion of something, but there are many other words and phrases that can be used as a substitute depending on the context. For example, "the rear" has a similar meaning and is commonly used in both formal and informal contexts. "The posterior" is a more scientific term that could be used in a medical context. "The hindquarters" is often used to refer to the rear of animals. "The tail end" might be used to describe the end of a line of people or objects. Other synonyms include "the reverse side" or "the flip side".