Style: Someone who has a consistent or distinctly unique way of dressing and doing things. Style is something that develops over time, and also changes over time. (Or at least is should -- dressing like we are 25 when we are 50 is not a good thing.) Style is the discovery of what looks good on our bodies and projects who we are.
Fashion: A general style of dress or particular clothing styles widely popular at any given time, accepted and in use by the majority. Without fashion we wouldn't have styles -- classic, traditional, athletic, feminine, etc. Including a fashion trend or two in your current style keeps you relevant and modern. Some trends become styles (i.e. boyfriend jeans), while others become fads (i.e leggings with cut-outs). It's about learning to recognize the difference between the two so you don't become a victim. Fads often include elements of design that aren't practical or may only be popular for a few months. Ask yourself: Does it support my current style or do I have to change my whole look?