Leakage is the amount of sound that escapes the headphones. This may be very distracting to the people around you, especially if leakage performance is poor and your listening volume is high. Fortunately, it doesn't matter as much for the secluded listener, as there's no one around to distract with leaking music.
We used the Overall Leakage @ 1ft test to obtain the leakage performance scores of the following headphones.
When it matters
If you plan to use your headphones within close range of other people, leakage should be of concern in your selection.
Poor leakage performance can be seriously disturbing to the people around you, especially if you listen to music at very high volumes.
However, for private listening sessions, leakage does not matter much and is sometimes encouraged in the design of headphones. Open back headphones take advantage of this to provide an open and spacious soundstage that feels more like speakers on your ears than like regular headphones.
Overall Leakage @ 1ft