label noise
The share of examples carrying the wrong label.
Label noise is the fraction of mislabelled examples; it caps what a model can learn and makes a test score a correct model as wrong.
Examples
If a third of the windows labelled "tap" are really a hand held still, the model learns that some stillness is a tap, and more training cannot fix it.
Labelling a video afterwards can mark both halves of a tap split across two windows as "tap", adding label noise.
See also