Lots of fights on the discussion pages about whether we should call the different world a "flash sideways" or "alternate timeline." It's a mistake to have that argument, as the solution is simple and is already on the Lost web site. The 'flash sideways' events are the transitions that take you to the 'alternate timeline'. Flash sideways is a verb, while alternate timeline is a noun. To even argue about which to use is to be confused about the language.
The Lost web page [] backs up this analysis. They refer to transitions between timelines as 'flash sideways'. When you hear that wooshing sound to the other timeline, you are experiencing the 'flash sideways'. That's a verb, it's something that is happening. This event takes you to the alternate timeline, alternate to the one you were just watching. The word alternate timeline is a noun.
Some have protested that calling one an alternate timeline is a mistake, as we can't give one priority over the other. That is a mistake. Nobody is saying one is an alternate, one is the main. They are both alternatives that we switch between via flash sideways events.
Why are people make this so complicated? Yes, the phrase 'flash sideways' is totally lame, but we are stuck with it. But the web site also makes clear that these events flip you between alternate timelines.
Enough. Link here in the discussions if you agree. :)
Note one implication of this fact: we can't call the no-crash timeline the "alternate" timeline. Even calling it the "parallel" timeline is a mistake, they are both parallel to one another, alternates to one another like yin/yang. So we need to have names. On the original page I suggested the 'crashless' versus 'crash' timelines, admittedly ugly. But we need a language to talk about this so if anyone has better names for the two timelines that would be cool.