Inside means in or toward the interior of something, the space contained within boundaries or walls. When you go inside a building, you move from the outdoor air into the enclosed rooms. Your lunch is inside your backpack, protected by the fabric and zippers. The batteries are inside the remote control, hidden beneath a plastic cover.

The word works as different parts of speech. As a preposition: “The treasure is inside the chest.” As an adverb: “Come inside before it rains.” As a noun: “The inside of the cave was dark and cool.” As an adjective: “She knew the inside story of what really happened.”

Inside often implies something hidden or not immediately visible. When you know the inside scoop about something, you have information that others don't. An inside joke only makes sense to people who were there when it started. Sometimes knowing what's inside matters most: a worn book might have a brilliant story inside, while a shiny new one could be dull.

The opposite of inside is outside, and together these words help us describe almost any location: inside the house or outside in the yard, inside your mind or outside in the world, inside the group or outside looking in.