What is an MHL port adapter?

"[T]he MHL port . . . is a normal microUSB port and works as one (a charger port as well). The MHL port enables USB On-The-Go. You'll need an adapter for that too (there isn't one in the box) but this one is fairly straight forward - you plug it into the Galaxy Note and plug a standard USB cable on the other end."
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Can someone please explain to me what type of adapter is necessary for the MHL port in order to use a usb flash drive with my Note II? (I absolutely don't have a clue what this refers to!)

The USB OTG cable is just the USB adapter that you plug into your micro-USB port.

Official Samsung version: [Only registered and activated users can see links. Click Here To Register...]

You can find significantly cheaper third-party solutions on Amazon and ebay and whatnot by just searching for "USB OTG" and "Galaxy S3" or "Galaxy Note 2" or something, but there's no guarantee on whether they'll work.

I believe samsung.com has one of those--and I considered ordering it; however, my mind was fuzzy about it because I've never even heard of an MHL port. Actually, I have several already, but I'm uncertain about the number of pins being different in the Note II so those I have mayn't fit . . .

Is this what you refer to?
HDTV Universal Adapter (11pin)

That's an adapter for micro-USB to HDMI, so not quite the same. It's similar, though.

There're two types of adapter cables that you're looking at (not including charging cables, of course): [Only registered and activated users can see links. Click Here To Register...], and [Only registered and activated users can see links. Click Here To Register...].

The former lets you output via HDMI, the latter lets you hook other USB devices up to your phone, with your phone acting as the host device.

Okay, that is what I initially thought this is! But then, I wasn't sure enough that I was correct. So, would the micro-usb-to-usb adapters I already have fit the Note II? (I mean, do they have the same # of pins?) I've been using these for other mobile phones, etcetera, for several years. Not sure how my mind got so messed up about this---perhaps the new (to me) terminology.

You might as well try, haha. If they don't work, then you'll need to get the 11-pin version. :)

Yo, but I'm fanatically cautious about port pins!