Here is something that I have been wondering about for a while:
If you strum all six strings of a guitar in standard (EADGBe) tuning what chord would you play?
I think it would be some variety of a E minor but I am not certain.
It's a mantra of mine that a given chord (or chord name) only properly exists in the context of a specific chord progression.
Thus, the name you give to the chord formed by the 6 open strings of the guitar depends on what key and mode you use this chord in. It might have one name if used in the key of A major, another name if used in the key of E minor, and so forth. And thus it is with all complex chords that go beyond the basic major and minor triads.
I think guitarists get entirely too hung up on giving a name to a particular grouping of notes that are strummed together. The individual pitches are what they are, but the name of the chord depends on how those pitches are being used at the time.
It all depends on which chord you want it to be. With GBD, you have a strong G tendency, and with the Es, that leans E minor. With the A, That's an added 4. So EminAdd4 (not suspended, because you still have the G).
But if you want to think of it as an A, With the A and E, you have the root and the fifth. The G is a dominant 7. The B is a 9th away from that E, and the D is again a 4th. No strong major-minor tonality, which can be good.
Back to the G. I said it has the full triad for a G major, with the A (2nd) and the Es, which are the 6th, so G69. Given some time, I could create some justification for it being some sort of Bminor9, too.
I'm sure that some of that is sloppy and not quite according to Hoyle, but the greater point is that chords are made out of notes and notes can be reconstituted into different chords.
There appears to be a lot of differing opinion as to what this 'chord' is. A lot of these reverse chord finders seem to either find 'A11' or 'Em7add11.' According to this source, the chord is Em7add11.
In the standard tuning (EADGBE) the open chord is A11/E. This means that it is an A chord, with the added 11th (D), 9th (B) and 7th (G) and an E note in the bass. A lot of chords like these are used in jazz. Also, Joe Satriani uses a lot of 11th chords in his songs.
Note, that this kind of notes for the open strings were chosen not because of the chord they create, but because it makes very easy to embellish other chords out of it.
I'v always heard it called an A11. And it never occurred to me that the C# is missing. Em7(add11) seems closer to the mark.
But pragmatically, whenever I use this chord, it is as an atonal "background" accent. That is, it's the chord I play when I want something that "doesn't sound like a chord." Mostly during rhythmic strumming of muted strings; un-muting one or two beats adds just a little bit of growl using tones that are effectively "neutral" to all keys; so it works in any key.
All the chord names suggested so far fail to convey the "hollow effect" of that stack of fourths with no "character tones" (3rd and 6ths) when you emphasize just the lower strings. I'm almost tempted to describe it just as figured-bass (if only I knew the "correct" notation): E\4\7\10\12.
It sounds like an Em11, it's probably because of the E in the bass. It does have the notes of G with an added 6 and 9. I tried to play it in different contexts, and it most often sounds like an E mainly because of the bass note.
Why don't you try it yourself, play some cadences in G, and A and Em (or any other key), and instead of landing on the tonic chord, strum the open strings and you'll notice that it fits best in the key of Em. There is a hint of G and even A in it but they are very unstable due the the inversion and missing note (A has no third).
When I play the A, G progression (mixolydian), after repeating the chords a couple of times to get the sound of the scale in my head, I can strum all strings without fretting instead of playing the G and it still sounds pretty close.
I guess it can function differently depending on the context. But when played alone, I definitely hear it as an E.
As others have pointed out, @user1044 in particular, context matters. If you're playing all the open strings in the context of some piece of music, you'd have to take the chord's role in the progression into consideration. Still, wouldn't it be nice to know what the candidates were?
Without resorting to "slash" chords, I listed every possibility below. These aren't equally good names for the chord, but each accurately describes the pitch classes in the chord (E A D G B). Chord symbols are bad at implying voicings, so, for example, Em7add4 and Em7add11 are both possibilities. Some people will tell you Em7add11 is correct because you can't have an "add" unless you use it with an extension interval (9, 11, or 13). Others will argue that the A2 is a perfect 4th—not a perfect 11th—from the E2; therefore Em7add4 is more appropriate. Whatever. There is no standards body for chord symbols. The conventions vary from publisher-to-publisher, genre-to-genre, and school-to-school.