Library sound is a term used to describe the sounds that are typically heard in libraries. The three most common library sounds are SHH, PSST, and SSH. SHH is an exclamation used to indicate that someone should be quiet. PSST is a sound made to get someone's attention without making too much noise. SSH is a sound made to indicate that someone should be quiet. All three of these sounds are commonly heard in libraries, as they are used to maintain a peaceful atmosphere.