The „C Major Seven Sharp Eleven“ is a Cmaj7 chord with an additional augmented 4th. Because the augmented 4th is not a part of the basic chord (consisting of root, 3rd, 5th, and 7th or 6th), it extends the chord and therefore it is written as a #11 in the chord symbol. While the number 4 at least occurs in sus4 chords, where the 3rd is replaced by 4th, a #4 is completely INEXISTENT in chord symbols.
A Cmaj7(#11) consists of C (1), C (3), G (5), B (maj7) and F# (#11). You will normally omit the 5th on the guitar, but if you play it, it must be lower than the #11 (e.g. CGBEF#), otherwise it will sound terribly dissonant (e.g. CF#BEG).
Maj7 chords are located on the first (I) and fourth (IV) scale degree of a major scale as diatonic chords (stacking 3rds using only tones of the scale). But only the IVth scale degree has an augmented 4th. Consequently Cmaj7(#11) is located on the IVth scale degree of the G major scale. The scale of the IVth scale degree is called the lydian scale. Therefore maj7(#11) chords are often called „lydian chords“. In jazz the maj7(#11) is sometimes also played on the first scale degree, like e.g. Dm11 G7(b13) Cmaj7(#11). In that style the harmonic relation of chords is often used to connect different scales in a very exciting way, like D dorian - G altered - C lydian scale in the shown progression.