The first page on a site.

To be more detailed, a "landing page" is the first page a user lands on in THEIR visit to a site. The term is frequently used to mean the page you go to after clicking on an ad.

It can also be used to mean where you land after clicking on a search result or on some other link on some other website.

I think tedsters latter description is the more appropriate. Landing Pages are typically the 'special' page that is written specifically for the PPC ad that is clicked (or the campaign).

I dont think many people call the default/index/home page the landing page much do they?

If you go to example.com directly, the first page is indeed the landing page. :-)

As mentioned if you're doing an ad program, don't make the home page the landing page unless the visitor finds EXACTLY what the ad advertises. For example, if you sell green widgets, the landing page should be example.com/green_widgets.html, not example.com/ or example.com/index.html.