From TalkBass Wiki
1) Generally meaning a "hot" or "high gain" sound, especially from a humbucking (double-coil) magnetic pickup. "In your face" as opposed to "smooth" or "mellow".
2) It can also refer to certain EQ characteristics such as a harsh top, grindy mids, or a woofy bottom
3) An attack which is hard, sharp, snappy, etc.
4) "Aggressive," when referring to magnetic pickup placement, usually refers to nearer the bridge, as in the Music-Man/Ernie Ball "Sweet Spot," rather than nearer the neck (as on a Jazz bass).
