Definition--Most often used to signify a state of mind, a way of thinking, or a feeling. Additionally, it is a position of the body, a way of carrying oneself, or in aerospace the orientation of the aircraft relative to the horizon.
Discussion--Attitude has moved from its original technical meaning in the fine arts of the position of the body to a technical term for the relative position of an aircraft. In day-to-day use, our attitude indicates how we feel about something, as in "I have a positive attitude about my test today."
In school, they say attitude is all-important. I was frequently told to "improve my attitude and apply myself". Unfortunately, they meant more than improve my posture, although that was bad too.
Etymology--Attitude comes from French where it was borrowed from the Italian attidudine. The Italian form comes form the Late Latin aptitudinem, meaning faculty. This comes from the Latin aptus, meaning joined or fitted.
Attitude was originally a technical term in the fine arts. In the 1700's the usage was extended to mean posture of the body implying a mental state. In the 1800's it was extended further to mean a manner of acting representative of a mental state.