Tear strength (BS 4303: 1968):

 

This test measures the force required to continue a tear which has already been started in the fabric. A cut is made in a rectangular sample to form two "tongues" and reference lines are marked to indicate the point the tear is to be continued to. One tongue is then placed in the upper jaw of a tensile tester, the other tongue in the lower jaw, and the two jaws opened to continue the tear to the reference line. The average tear strength is then calculated.

Again, BS 2543 specifies minimum tear strength for different uses:

Occasional domestic/Light domestic = 15N
General domestic/Severe domestic = 20N
Severe contract = 25N