.lrc is a file format for synchronizing lyrics with music, and specifically with digital audio files such as mp3's, ogg's, or midi's, among other filetypes.  The .lrc file format is supported by some digital players as well as rockbox (with the correct plugin).  The .lrc file format is also useful with music on the computer as virtually any player can be run with Minilyrics, which displays the lyrics of your music as you play it.  

The format of the .lrc can also be stored in the /sylt/ tag of an mp3 file.  Minilyrics has the capability of saving .lrc information into the mp3 tag so that a physical .lrc file is not needed to display lyrics with the song. 

 .lrc's generally follow this format:

[offset:1000] 

[ar:Sting]
[ti:Something the boy said]
[al:Ten Summoner's Tales]
[by:nohitter151]
[00:31.98]When we set out on this journey
[00:36.33]There were no doubts in our minds
[00:40.31]We set our eyes to the distance
[00:43.67]We would find what we would find

Where offset, ar, ti, al, and by are all optional tags for the files.  Offset will offset each timestamp by the following number of milliseconds.  By is just a recognition of the user that created the .lrc file, my handle for uploading lyrics is nohitter151.  Each line of lyrics displays at the time listed in brackets as the song plays. 

More information on the .lrc fileformat can be found here.