Ham is the term used to describe unwanted email that clogs up your inbox like spam, but isn't strictly-speaking spam. It typically takes the form of mailing list traffic that you signed up for but can't figure out how to unsubscribe from, or advertising from a company you once did business with online.
For years now, I've been subjected to the occasional bit of ham from LinkedIn reminding me of this or that invite I haven't yet replied to, or a message I haven't read yet.
Lately, I've noticed a fair amount of actual spam coming in designed to look like LinkedIn ham. The layout, artwork, and subject line are similar to the "You have a pending message from X" messages I frequently get from LinkedIn, but the link takes you to a phishing site.
The key signs that it's a fraud are the From: line which is typically gibberish, and the Subject: line which is just a little bit off, but these will likely be fixed as the phishers refine their fraud. Ultimately, the best defense is the practice you should be using on all emails: always hover over a link before clicking it, and make sure it goes where you think it does.
Be careful out there, you hear?