A spirit is considered to be the part of a being that is not the body. Other words with the same meanings are soul and ghost. When a body is alive, it has a spirit in it. Death is when the spirit separates from the body.
Christians believe that spirits exist in Heaven or Hell. (See 1 Timothy 3:16, 4:1)
Spiritualists believe that spirits can talk with people, or change things in the world. Many religions forbid communicating with such spirits in any way, (see Leviticus 19:31) but a few include this as part of their practice.
Another use of spirit means the main purpose or meaning of a sentence or document. For example, the "spirit of a law" is the true meaning of the law which the creator wanted. This phrase is often used when the words and sentences of a law could mean more than one thing, but a judge must decide what meaning is correct.