Viewer 2 Quick Start Guide/Inspectors
From Second Life Wiki
Inspectors are temporary, context-sensitive control panels that appear when you hover your mouse cursor over an avatar or an interactive object. Inspectors are designed to help you explore and interact with the world around you; they provide you with brief details about an avatar or object, and give you access to many options for interaction.
Notably, opening an Inspector for a Resident who has voice enabled allows you to adjust the volume of that individual Resident's voice communication.