Wow, this is pretty confidential... Anyway for those of you wondering:

HK - Confirmed paying passenger no seat (as stated above)
SBUP - Standby Upgrader (as stated above)
PSUP - Positive-Space Upgrader - Usually an employee traveling for work purposes or attending something they need to get to for the airline and they deside to upgrade.

S1, S2, S3, S3B, S3C, S3D, S4 are all for employees/employee tickets.

S1 - Employee emergency pass
S2 - Employee higher-priority pass (limited number avail.)
S3 - Regular active employee pass (unlimited)
S3B/C/D - Retired employee/Non Dependent child
S4 - Buddy Pass riders.