What is the lock symbol with a circle/arrow around it?

"A padlock with a circular arrow around it in the status bar at the top the screen means that the phone is locked in portrait mode and will not rotate to landscape mode. This can be turned on and off by double clicking home so that your open apps are displayed. Then, swipe these icons to the right until your iPod controls appear, where you should see an icon with a circular arrow. This icon locks your screen rotation. Good luck and I hope this helps!

UPDATE

I was asked to update this answer because the method has been modified to something very similar with the advent of iOS 7. You now have to swipe up to bring up the control center and then click the lock/unlock icon on the top-right of the menu to engage/disengage the screen lock. (Thank you Miro & iFixers :-)"

Get rid of the lock by just sweep your finger from bottom to top. It's like a shortcut. It is the very last button from left to right.

When your iPhone 5 is locked double click the home button, using your finger or thumb swipe from the bottom of the screen to the top of the screen, the control menu appears and you click on the icons to activate or deactivate them

Slide your finger from bottom of the screen to top of the screen fast. (Same way to access you flash light or camera now) and you'll see it on the top right corner of screen. Very easy to do.

for the iphone 4, which didn't seem to be addressed: go to settings. go to control center.swipe from bottom to top hard and fast. a gray screen comes up with that icon in upper right hand corner. tap it once and you're landscaping will no longer be locked!

Just swipe up from the bottom of your home page, then touch the rotate lock icon in the upper left corner. It's that simple! Someone should inform verizon associates because I went there and no one, not even the store manager knew how to fix the problem. Thanks oldturkey 03.