There's a bit of a tale behind this one. It's a portmanteau of the words "jam" and "portfolio". The portfolio part being that I made this site in order to showcase my creative and professional work. (If you're here because I gave you my resume, thanks for checking it out! :D)
But what about the "jam" part? That's where the aforementioned tale becomes more personal. My parents gave me the nickname "J-boy", for reasons that are completely inscrutable. Out of all the nicknames I had been given, that one stuck the most. Of course, as I got older, around age 12, I wanted to be more "grown up" and "mature", so I tried to change it to "J-Man" (Which didn't stick with my parents, or anyone else, for that matter.) Then, when I was 13, one of my friends convinced me to play Roblox with him, and I had to make an account. So I made my username "TheEpicJman".
You could definitely tell a middle-schooler came up with that, I know, but at the time, I was was very attached. At least, I was attached until I forgot the password to the account. But I continued to use the name on several other platforms.
The weird thing about the word "Jman" is that whenever you tried to type it really fast, you would usually write "Jamn" instead. Eventually, I grew out of the name, and around age 16, I thought to myself, "Hey, that would be kinda funny if I dropped the "N" and my name were actually Jam". So I took a picture of a jar of Smucker's strawberry jam off of Google Images and drew a silly face on top of it in Paint Tool SAI and made that my new avatar.
Both me and all my friends liked it, thought it was hilarious, and it stuck.
So, "Jam" was less of a spontaneous conscious choice than an evolution, growing along with me through childhood, middle school, high school, and now college. I'm extremely happy with it now, and I don't think it's going anywhere anytime soon. But hey, I'm open to change.