The standard grips this chord is usually shown with.
Balt is B, D#, G, A and C, a altered dominant. The shape this page opens on is written x21441, lowest string first.
Note by note. B is the root, D# is the major third, G is the sharp fifth, A is the flat seventh and C is the flat ninth.

Also written B7alt, B7altered or B altered dominant. The same chord either way; which spelling you meet depends on who wrote the chart.
There are 9 common shapes for Balt on the guitar, and 20 derived voicings in 2 families.
One note away. Change a single note of Balt and you have Baug7 (with one note taken away), Baug9 (with one note moved) or B7b9 (with one note moved).
The common shapes, written lowest string first: x21441, x2344x, 76x867, 78980x, xx9867, 7898x7, x-x-9-10-0-11, x-x-9-10-12-11, x-14-13-x-12-13.
Under the hand. None of the shapes for Balt uses an open string, so every one of them is movable; the lowest sits at the 1st fret. None of them needs a barre. Together they cover the neck from the 1st fret to the 14th.
Where it goes. Balt is a dominant with its tension raised, so it still points at E — harder than a plain seventh does, because the altered tones sit a semitone from where they are going.
Shell. Root, third and seventh: the guide tones fix the quality, so the fifth is dropped. That is what leaves a string free, so pick a tension to put on top. Balt has x2121x, 7675xx, x-x-9-8-10-8, x-14-13-14-13-x, x2x243, 7x788x.
Rootless. The root left to the bass player. Frees a finger for a tension. Balt has x0101x, xx1213, xx5545, xx7888, x-10-10-8-10-x, x-x-10-12-10-11, x-12-13-12-13-x, x-x-13-14-13-15.
Tensions. A shell of Balt, root, third and seventh, leaves a string free, and the tones that belong over it are the #11 (E#).
What kind of chord this is. Balt is an altered chord — a dominant seventh with its fifth or ninth moved. altered dominant chords on every root, and what they are for.
The common shapes and the derived voicings come from different places, and both are explained in where the chords and the theory come from.
Shows each chord the way this style would voice it, and marks which of its alternatives belong to the idiom.