The middle of a grading spectrum. For example, in most American schools, a 100 point grading system is used. Therefore 50 would be the "Senay Line". This term comes to us by the educational philosopher Mike Senay who reminds us that "50 is half of 100".

the thing that you don’t have when you’re phones percentage is over 20

In school, and other areas where grading is based on the 100 point system; The Senal Line is considered a 50. Those scoring higher than a 50 are said to have "passed the Senay Line" those going below it "falling below the Seany Line". It is named after Mike Senay, a genius whos theory was that a 50 should be considered average as it is right in the middle.