借光 (jiè guāng) is a polite fixed expression used to ask for a favor, to excuse yourself when passing through a crowd, or to request someone's help. It literally means 'borrow light,' harking back to an old story. In modern Chinese it functions like 'excuse me' or 'may I trouble you' — less formal than 劳驾 but still courteous. You can also insert 个 between the syllables (借个光) for a slightly more casual tone.