The Free On-line Dictionary of Computing (30 December 2018):

Euclidean norm

    The most common norm, calculated by summing
   the squares of all coordinates and taking the square root.
   This is the essence of Pythagoras's theorem.  In the
   infinite-dimensional case, the sum is infinite or is replaced
   with an integral when the number of dimensions is
   uncountable.

   (2004-02-15)