Meaning of "ham" in the context of Spam Classification

I am studying e-mail spam classification, and I have encountered the word "ham". I wonder the meaning of this word. The meaning of ham is as follows:

ham (h4m) n.
1. The thigh of the hind leg of certain animals, especially a hog.
2. A cut of meat from the thigh of a hog.
3. The back of the knee.
4. The back of the thigh.
5. hams. The buttocks.
6. An actor who overacts or a performer who exaggerates.
7. A licensed amateur radio operator

There is a paragraph that I cannot understand:

Business Problem
Spam emails are something we’ve all experienced. Spam mail, often known as junk mail, is an email that is sent to a large number of people at once, sometimes with cryptic messages, scams, or, most dangerously, phishing information. The problem here is that the email needs to be classified as spam or ham based on the content of the mail.
...
3. The “Email Text” column contains the email header, subject, and content. The “Target” variable 0 represent “not spam” and 1 represents “spam”. The ratio of ham to spam class is 67:33 this is an imbalanced dataset. [1]

What is ham in this context?

[1]: https://medium.com/@yesprabhakaran98/email-spam-classification-92b661d3b700

"Ham" is any email that is "not spam". It's just quicker than saying "not spam" or "non-spam".

(It helps if you know what "spam" refers to in the context of meat.)