A contracted/honorific form of いらっしゃる used as an auxiliary (often after the -te form) to show respect, meaning 'to be (doing)' or 'to go/come' in honorific speech.
先生は今、研究室にらっしゃるそうです。
I heard the professor is in the lab right now.
今、何してらっしゃるんですか？
What are you doing right now? (polite, honorific)
お客様がすでにらっしゃっているので、どうぞお通しください。
The guest has already arrived, so please show them in.