In Wikipedia there is a page on hybrid cryptosystems. However, although cryptography contains a lot more than just encryption, only hybrid encryption using key encapsulation and data encapsulation is discussed.
So my simple question is: should I consider a signature scheme using a hash a hybrid cryptosystem? Or is the term not that well defined and is it up to the entity that uses the term?
What I didn't directly see is that a hybrid cryptosystem is not the same thing as hybrid cryptography. A cryptosystem is commonly targeting encryption: it exists of a key generation function $\operatorname{Gen}$, an encryption function $\operatorname{Enc}$ of course a decryption function $\operatorname{Dec}$.
So although signature generation could probably be called hybrid cryptography, it commonly isn't a hybrid cryptosystem because it lacks the $\operatorname{Enc}$ and $\operatorname{Dec}$ function.