Different definitions for spam, and I think people use separate ones on different occasions. For example, one could be taking quantity over quality. Or just making low quality posts in general.
Spam meaning was not really intended to what you guys gave meaning to. Spam was originally unwanted Emails. Forums had later adopted the meaning for someone who constantly posts junk messages. Message could even be high quality but anything that is not related to a topic can be spam, spam is unwanted advertising. Mrprep meaning of spam is the TOS.