Plane lands, some people get off, some people get on, flight continues - just like buses or trainsEdited: 1:58 am, July 16, 2013
Stopovers are longer than 24 hours as a definition.
A very very good question, as you're raising the whole issue of airline speak.
Flight numbers do NOT necessarily mean non stop services. They can be referred to as "direct" but that's not non stop. In your case case sounds like the flight originates in San Diego (SAN) and flies to Portland (PDX), but with a stop (not a stopover) in Fresno (FAT). That, in airline speak is referred to as a"direct" flight, even though it's not non-stop.
So you will have a stop, possibly staying on the aircraft, possibly having to change to another en route to PDX. In all likelihood in your case, as FAT is a small airport, it would be the same plane, you'll unload some pax, pick up others, and continue to PDX.
BUT, that isn't always the case. For example (and all airlines do this so this is just one example I know of), United 837 from San Francisco to Bangkok has a stopover at Tokyo Narita, and often a plane change (747 to 777), and you must deplane, reclear security and re-board. AND, If the inbound to 837 to NRT were badly delayed, the onward flight to BKK may still depart, not waiting for the inbound flight (and pax) on the same (direct) flight number.
The other issue that raises its head is frequent flyer credit. "Direct" but one stop flight numbers give you frequent flyer miles based on the non-stop mileage, even though you have flown more miles and had he inconvenience of landing somewhere else en route.
So, while you may not have to worry too much, the concept of "Direct" vs "Non Stop" needs to be made clear.
PS (and a big one) - Can't you get a non-stop from SAN-PDX on Alaska (Delta code-shared)? Much easier and convenient than this "direct" flight you have now?Edited: 2:56 am, July 16, 2013
Thanks for the explanation USBusinessTraveller. I haven't booked the flights yet as I can't get the right combination of price, times and layovers, that and I can't make a decision to save my life, so I will keep looking.