Bacterial Artificial Chromosome (BAC) is a well-known molecular biology tool used to clone large segments of DNA in bacteria. BACs are widely used in research, diagnostics, and biotechnology. However, there are several synonyms for the term BAC that are used interchangeably. Some of them include Bacmid, Cosmid, Fosmid, P1 Artificial Chromosome (PAC), and Yeast Artificial Chromosome (YAC). These synonyms were developed to improve the efficiency of cloning and manipulation of the DNA fragments. Each synonym has unique properties that make them ideal for various applications. As such, scientists can select the most appropriate synonym depending on their specific needs.