According to Urban Dictionary, human spam is "Individuals who approach one on the street with unsolicited literature or requests, such as free newspapers, The Big Issue, flyers, requests for money, 'Charity Muggers', religious apologists, petition carriers, etc. These individuals in Britain have replaced the now banned practices of cold calling, email spamming and junk mailing, as the only thing charities/companies don't need permission for any more is invasion of personal space and public harassment." This focuses on the in-person aspects of human spam but it can also be related to online.
You see it all the time via twitter, tumblr, and other social media outlets. Human spam is annoying, off-putting, and is not a good way to showcase work. Showing your work is important, but finding a balance between spamming and showing in a not annoying is also important.