In Thailand there is no differentiation between rules and they only have what we would term full rules.. i.e elbows, knees to the head etc. In this country we tend to bring people along a more gradual path with a progressive step toward full rules. Novice bouts will, as the name suggests, be for first timers or people with only a couple of fights and these won't include elbows or knees to the head but are generally still over 5 rounds of 1.5 minutes there is some ambiguity with c class rules as they are generally 5 rounds as well, also of 1.5 minutes, also without knees to head or elbows and sometimes still with shinguards but I think this depends on the show and the promoter etc. B class fights are fought over 5 x 2 minute rounds and now include knees to the head but still no elbows and no shinguards and finally A class fights are fought in accordance with the recognised standard for Muay Thai of 5 x 3 minute rounds with a 2 minute interval between rounds and the use of both knees to the head and elbows and obviously no protective gear beyond gloves, groin guard and mouth guard. If you fight in Thailand you will fight full rules though if you train at a reputable camp you will be evenly matched. If you fight in this country you will fight novice or c class first and move through the classes at your trainers discretion depending how well you do. The other term you mentioned, oriental rules, is a kickboxing term and they have several different rules within that sport as well. Hope that helps as a general guideline