TITLE: The hookrightarrow and its meaning
QUESTION [10 upvotes]: 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!

REPLY [6 votes]: In an algebraic setting, $\hookrightarrow$ denotes a monic map and $\twoheadrightarrow$ denotes an epic map.