So I ended up talking with an ex-military guy yesterday who was a radar/mapping specialist. Basically, he knew exactly what that number (4326) was, where it came from, and why it is there.

It is an industry standard for computing geography. The problem is that the earth is not a perfect sphere (it bulges in the middle), and SRID 4326 accounts for that.

As I stated, the table sys.spatial_reference_systems lists all of the code and what they are. But the short version is that you are really only going to use 4326 unless you have a very specific reason to use something different.