I first wrote about this kind of nonsense back in 2008, and this is STILL NOT A HOLOGRAM:
Tupac here is being displayed using the Musion system. Musion has intentionally and wrongly marketed their system as a "hologram", possibly to divert attention from the fact that what they do is simply a modern version of a 150 year old visual effect: Pepper's Ghost. The Musion system is cool, but their innovation is simply coming up with a better mirror (they use a thin film instead of the heavy glass used 150 years ago).
From wikipedia, with a hologram, "The image changes as the position and orientation of the viewing system changes in exactly the same way as if the object were still present, thus making the image appear three-dimensional." So the Musion system is NOT a hologram, because if you walked across to the other side of the audience at the Coachella show, you would NOT see the side of Tupac's head, because you're simply looking at a 1/2 transparent movie screen.
As far as I know no one has yet created a viable, large scale "volumetric display", which many seem to think is real because they saw it in Star Wars:
Here, this film trick shows what a volumetric display (3D Hologram) would look like. As the viewer's viewpoint changes, we see different perspectives of Princess Leia. The number of people who think this is real is always shocking to me, because you know what else was shown in Star Wars that you can't buy today? Light sabers. We'll likely get them before we get a 3-D "hologram".
And if you want to read a great book about the fascinating history of Pepper's Ghost, get Jim Steinmeyer's Hiding the Elephant: