Definition of a splitting field of a finite group

Question

This is a basic question from the journal 'Mathematische Zeitschrift' 208 (1991) page 243.

Let $K/F$ be a finite Galois extension of number fields and $G={\rm Gal}(K/F)$. Also let $L$ be any number field, $E$ a finite Galois extension of $L$. The article then states that $E$ is assumed to split $G$.

Question: What does it mean by a field splitting a group?