Posture refers to the general shape, carriage and attitude expressed by the body.
'Posture' is also used to describe the dominant belief or mental attitude that is assumed by someone.
Given that we express our mental states and attitudes through our bodies, the word 'posture' neatly incorporates both the mental and physical aspects of how we present ourselves to the world and is an example of how our psychophysical state influences our general use and functioning. It is possible to gain some considerable understanding about another person’s mood, attitude and use, just by observing their posture and body language.
However 'posture' tends to refer to a static position, rather than the whole use of the body during movement as well. Some practitioners from other disciplines refer to a person's 'dynamic posture' when thinking about their alignment and movement patterns. This term moves closer to Alexander's concept of 'use' but is not the same.
Many people come to Alexander Technique lessons in order to 'improve poor posture', which contributes to problems such as back pain and RSI. Whilst it is true that most people do bring about changes in their posture, these are the result of learning how to stop and let go of the old habits of mis-use that we all tend to have, that contract and distort the body during movement and rest.
Improvements in our use allow us to return to some of the poise and freedom of movement that most of us were fortunate to have as children, before we developed habits of mis-use and poor posture, or experienced accidents to our body that threw us off balance.