What is the difference among col-lg-*, col-md-* and col-sm-* in Bootstrap?

Question

What is the difference among col-lg-* , col-md-* and col-sm-* in Twitter Bootstrap?

Answer 1

.col-xs-$   Extra Small     Phones Less than 768px 
.col-sm-$   Small Devices   Tablets 768px and Up 
.col-md-$   Medium Devices  Desktops 992px and Up 
.col-lg-$   Large Devices   Large Desktops 1200px and Up