A $p$-group $G$ is said to be special $p$-group if $Z(G)=[G,G]=$ elementary abelian.
A $p$-group $G$ is said to be extra-special if $Z(G)=[G,G]=$ elementary abelian of order $p$.
The questions I am considering are not too much technical; it is about terminology, and some history. Also, I didn't find any reference for them in old books of Group Theory and algebra. I couldn't ask to anyone around me, as they are experts in subjects other than Algebra, hence posted here.
Q.1 When the terminologies of special $p$-groups and extra-special $p$-groups were introduced?
Q.2 Is there any reason why special $p$-groups are called special? (I mean, Groups with certain interesting property may be termed as special, but what is reason to call special $p$-groups as special?)