The lydian scale is the mode built off the fourth note of the major scale. It differs from a major scale because it has a raised fourth note. The characteristic note is the #4 and although it doesn't need to be avoided, it does make the scale sound very colorful. This is the scale to play on any major scale that isn't the Imaj7 and it sounds beautiful every time. Also it is a classic ending chord to songs in major keys. When you play that final major chord, just go up and hit that #11 (same as #4) and the song will sound cosmically finished.