The hookrightarrow and its meaning

Question

Very weirdly I found a $\hookrightarrow $ in my Algebra book just like that. Could someone please just tell me what it means? Sorry for this maybe stupid question in advance but very much appreciate your help!

Answer 1

Resolved in comments, so I'll make this community wiki. $F \hookrightarrow G$ denotes the inclusion of $F$ in $G$, with $\hookrightarrow$ denoting a monomorphism.

Answer 2

In an algebraic setting, $\hookrightarrow$ denotes a monic map and $\twoheadrightarrow$ denotes an epic map.