Support 

Breathing...the most natural thing in the world...until students have a flute in their hands! I love Michel Debost's concept of breathing (the inhalation) and blowing (the exhalation). Once students understand the correct way to inhale (using the whole body: rib cage expanding in all directions, shoulders stay low and a relaxed abdominal area) we are halfway there. This post is really about what happens on the exhalation! I love having students take a breath and exhale with a sigh to demonstrate an unsupported exhalation: the air is rapidly expelled, and has a natural diminuendo as well: the opposite of what our breath for flute playing should be doing. Next, take a breath and exhale making a strong 'hissing' sound: students will automatically engage the muscles in the abdominal area. (the same engagement happens when we cough or sneeze: the body knows what to do, we just need to make sure it happens at the correct times). 
Support is that feeling of a slight pushing out/down in the abdominal area as well as the intercostal muscles in between the ribs. We need to keep the pressure as stable as possible when we are blowing out: we want our phrases to be long and flowing! Support of the air column is the way to achieve this.