Aggressive and passive refer to the amount you bet in any given situation. The more you bet the more aggressive you are. Most professional poker players recommend a tight-aggressive general playing style. The truth is your playing style should be flexible. You need to be able to adapt your style to fit different situations, for instance a ten player sit and go should be played differently then a three hundred player tournament. Table position should also be taken into consideration when determining your level of aggression in a hand. Also you need to be able to react to the other players and their styles.