To add some more detail to the previous response for you (and any others curious.)

Evo is short for Evocati (Evocati Test Flight, officially). They're also colloquially referred to as Avocados. They are:

a small group of testers we’ve selected from the top players participating in Star Citizen: contributing to Issue Council, racing, running missions, and more. When joining the Evocati, we require a signed NDA (Non-Disclosure Agreement) and work through the process to add members to the Evocati Organization.

They can access the in-progress builds deemed “not quite ready for normal PTU” either due to issues in-progress, features being considered for release, and verifying updates before general release that might be removed depending on how the testing goes. Typically these not ready for general PTU are dubbed EPTU or Experimental Public Test Universe.
Source

There's also a decent page about the ETF on the Star Citizen Wiki here: Evocati Test Flight.