flatline

Short definition from Wiktionary

Noun

1. 1
   An asystole; the absence of heart contractions or brain waves: The disappearance of the rhythmic peaks displayed on a heart monitor.
2. 2
   An asystole; the absence of heart contractions or brain waves: The disappearance of brain waves on an electroencephalogram.
3. 3
   An unchanging state, as indicated in a graph of a variable over time.
4. 4
   A line that is run low to the water from the rod tip, generally off a release clip of some type.

Verb

1. 1
   To stop beating.
2. 2
   To die.
3. 3
   To kill.
4. 4
   To remain at the same level, without development; or, to fall.
5. 5
   To experience significantly decreased rates of change compared to previous rates of change.
6. 6
   To fish using a flatline.