{ x|.....} means the set of all values of x that satisfy condition ...
My German isn't the best but I would say that "M" consists of all values of x that satisfy all of conditions \(\displaystyle E_1\), \(\displaystyle E_2\), \(\displaystyle E_3\), …, to \(\displaystyle E_n\).
For an English example, {x| x^2= 4} is just {-2, 2} since -2 and 2 are the only numbers whose squares are equal to 4.