to be; to come; to go (polite version)
いらっしゃる is a polite verb used as the honorific form of いる, くる, and いく, meaning 'to be', 'to come', or 'to go', respectively.
いらっしゃる is an honorific verb that raises the status of the person you are talking about. Use it when the subject is someone you respect, such as a customer, teacher, or elder. It can replace いる (to be/exist), くる (to come), and いく (to go). For example, instead of saying 先生はいます (a teacher is here), you say 先生はいらっしゃいます. Similarly, instead of saying 田中さんは来ます (Tanaka-san comes), you say 田中さんはいらっしゃいます. Note that the meaning depends on context, so you must infer from particles or situation whether it means 'is', 'comes', or 'goes'.