inside
"Inside" is a very common and useful word in English. It works in several different ways — as a noun, adjective, adverb, and preposition — so it covers a good range of meanings. Here are the most important ones.
When something is located within the boundaries of a place, object, or container, you say it is 'inside' it. Think of a letter inside an envelope — the letter is completely surrounded by the envelope.
everyday language · Modern, widely used