Thanks for the comments everyone.
A mortised handle is a full tang handle where instead of drilling and filing out a slot for the tang, you split the handle block in half, remove material from both halves, then glue them back together around the tang. This is the first mortised handle that I've done, and the friend I made this knife for agreed to test it out for me. I first heard about this type of handle construction here on the forums, and some very good makers use it occasionally including one of my knife making heroes, Matt Lamey. Theoretically, this lets you have a more substantial tang, and a better fit with the handle. On this knife, the tang could almost be a full tang as it's 4.5" long and 1.125 wide all the way down the handle. My only concern is that the joint in the wood might separate with heavy chopping. My friend has been warned and will let me know, however, I did test it pretty hard before I sent it too him and had no problems.