What are measurements called that fall beyond three standard deviations from the mean?
Measurements. Just because a particular result lies far from the
mean doesn't make it any different. If it's noticeably far from the
"crowd" of all the other measurements, it can be called an outlier.
An outlier isn't necessarily bad, just different. It should be
examined in detail to see if there's something odd about it, but
not discarded out of hand.