What category should I use for my W2 in box 14 it has SevPay1 for the amount of $12336.24.

Yes, you can select Other (not classifed), since it doesn't match a description on the list. 
 

Use "Other (not classified)" or don't even enter it. It looks like it's telling you how much severance pay you got. But the severance pay is included in box 1. The entry in box 14 is just for your information. It doesn't affect your tax return.