# Acoustic, optical, ferromagnetic and antiferromagnetic spin-waves?

In the context of spin-waves I have seen the following words as descriptors*:

• Acoustic
• Optical
• Ferromagnetic
• Antiferromagnetic

which I have seen used together e.g. "acoustic ferromagnetic spin waves" as well as individually e.g. "antiferromagnetic spinwave". I am assuming that acoustic means the dispersion relation goes to zero (see my related question) as $k\rightarrow 0$ whilst optical means it does not. But I am yet to find any clear cut definition of what the qualification of Ferromagnetic and Antiferromgantic mean. Please can someone explain this to me?

*The source is not in the public domain but a quick search on your favorite search engine should bring up sources with the individual terms.