What does high value of weibull modulus indicate?

The Weibull Modulus is related to the distribution of flaws in a brittle specimen. It is important to note that it isn't relate to the size of the flaws.

To find the Weibull Modulus, many samples of the same material are tested, in tension, to failure. If the flaws are evenly distributed throughout the specimen, the data from the the tests will show little statistical scatter and result in a high value of the Weibull Modulus.

Conversely, if the flaws are unevenly distributed causing the test data to differ greatly from sample to sample (greater flaws means more opportunities for stress concentrations at those flaws, causing a lower failure stresses) then there will be large statistical scatter in the test data, and the Weibull Modulus will be measured as a lower number.