What is the meaning of "fix" in field theory?
Example: I found a definition of field automorphism,
A field automorphism fixes the smallest field containing $1$, which is $\Bbb Q$, the rational numbers, in the case of field characteristic zero.
The set of automorphisms of $F$ which fix a smaller field $F'$ forms a group, by composition, called the Galois group, written $\operatorname{Gal}(F/F')$. For example, take $F'=\Bbb Q$, the rational numbers, and ...