FIOS G1100 Router has two WIFI connection choices, why?

Searched for the forums to see if this was already asked but did not find anything.

Just hooked up new FIOS G1100 router.  When connecting from a wireless device (e.g. IPad) I'm seeing two choices.  One with a "-5G" extension, one without.  Whats the difference?  What should I use when?

Note that I took the default configuration out of the box.  No changes.

Thanks