An active episode of a chronic or recurrent disease.
(music) The onset of a musical note, particularly with respect to the strength (and duration) of that onset.
(audio) The amount of time it takes for the volume of an audiosignal to go from zero to maximum level (e.g. an audio waveform representing a snare drum hit would feature a very fast attack, whereas that of a wave washing to shore would feature a slow attack).
(soccer) One of the players on a team in football (soccer) in the row nearest to the opposing team's goal, who are therefore principally responsible for scoring goals.