Kerosen
For SIA the P1/US hours are those hours that you have flown on a multi crew aircraft and although not the pilot in command, (Captain), you have flown that sector including the take-off and landing under the supervision of the captain.
P2/US would be those hours when, as a second officer, (P3), you have carried out the duties of the co-pilot under supervision. If you were ever a cadet pilot some of those hours would probably be classified by SIA as P2/US.
Once you have completed the hours and experience form be sure to copy it and keep the copy as you will be asked to give all that information again at least once. It is a check to see if there are any gross differences etc.