In astrology, a progression is simply the way that the planets move around your natal birth chart. Your natal chart indicates your character and your potential, while your progressed chart is calculated by your astrologer using a centuries old method.
Your natal chart will always be the same, but your progressed chart will change for every year of your life. Progressed charts are useful for understanding changes in your life and your personality, and getting a hint as to what may be happening in that particular year. Progressed charts are not to be confused with a solar return chart, which is calculated for the anniversary of your birth and uses a different procedure.