As to is a phrase that means “concerning” or “regarding.” When you say something as to a topic, you're pointing out what subject you're talking about.

If your teacher asks, “Any questions as to tomorrow's field trip?” she's asking for questions about the field trip. When a detective investigates a crime and says he has doubts as to the suspect's alibi, he means he's uncertain regarding whether the alibi is true.

The phrase often appears when someone wants to be precise about which topic they're addressing. A scientist might write, “As to the question of whether plants feel pain, current evidence suggests they do not.” A parent might say, “As to your request for a later bedtime, let's discuss it this weekend.”

You'll sometimes see as to when people introduce a topic they're about to explain: “As to how we'll organize the teams, I'll put names in a hat and draw randomly.” While you can often replace as to with simpler words like “about” or “regarding,” the phrase has a slightly formal tone that can make your writing sound more precise and thoughtful.