Originally Posted by BenjaminNYC

HIP = Higher Interpoint Price.

Cerain fares are "Routing Fares". That means that you have to take one of many specific routes. So, for instance, a JFK-NRT fare would allow transit in only IAD/ORD/SFO/LAX. (Just an example; I have no idea about JFK-NRT fare). They also usually spcify no stopovers.

Other fares are "MPM Fares" (MPM = Maximum Permitted Mileage). This means you can take ANY routing you want, through pretty much any city, but you cannot exceed XXXX miles. These fares allow unlimited stopovers. HOWEVER, these fares are subject to HIP check. What that means is that if you stop over in a city in between your O & D, which is a more expensive market, the ticket will be re-fared for that market.

Example (illustrative):

D class fare JFK-BKK = $5000
D class fare JFK-NRT = $10000

I can travel JFK-LAX-NRT-BKK with no stopovers for $5000. I can choose pretty much any routing under the MPM. HOWEVER, if I stopover in NRT, the ticket will be repriced at the JFK-NRT fare of $10000, since NRT is a Higher Interpoint Price.

Essentially means no-stopovers in more expensive cities.