Question about the @media screen query

When you specify an orientation - as in the sample query below - what is that supposed to accomplish? Does it not even allow the webpage to load unless the device is held in landscape fashion? Or will it display in landscape only, even if held in portrait fashion? I'm just not sure what specifying the orientation is supposed to accomplish . . . and figured it would be easier to "ask the experts" rather than doing a bunch of testing. (I'm kind of a novice html and css guy . . . and have been "out of the loop" for a while when it comes to writing code.) Thanks!

/* iPads (landscape) ----------- */
@media only screen
and (min-device-width : 768px)
and (max-device-width : 1024px)
and (orientation : landscape) {
/* Styles */
}