The B lydian dominant seventh chord is a 5-note chord consisting of the notes B, D#, F#, A and E#.
You can see these notes highlighted in the interactive piano chart below.
The chord itself is often abbreviated as B7#11.
Interactive piano diagram for the B lydian dominant seventh chord
Chords that are a subset of B7#11. These contain less notes but all of them are included in B7#11.