Someone or something aggressive shows a lot of energy and has a strong impact. After the aggressive salesman stopped them again on their way through the mall, the couple got aggressive and replied in a loud, made-up foreign language until he went away.
Being aggressive often means being physical or showing force, but it is equally powerful as an adjective reflecting a forceful determination to get something done. An aggressive football player may tackle everyone in sight to get a win, while a driven student might tackle a project or problem head-on with aggressive determination to improve their grade. Aggressive comes from the Latin aggress-, "attack," and being aggressive shows an intention to attack bodily, mentally, or verbally whatever gets in the way.