Yegg is a slang term for a burglar or SAFECRACKER, someone who breaks into safes to steal money or valuables. It is derived from the word 'yeggman, ' which was popularized in the early 20th century. Safecrackers are highly skilled professionals who use a variety of tools and techniques to open safes without damaging them. They often work with locksmiths and security experts to gain access to secure areas. Safecracking is a dangerous profession and requires a great deal of skill and knowledge.