Evocati (from lat. evocatio, "summoning", name of reactivated veterans in the Roman Empire), also known as Avocados is a term for a group of circa 800 players (as of November 2016), who are voluntarily playtesting Star Citizen's content for future updates of the game before they are released to the Public Test Universe. They are appointed and invited by CIG, based on their contributions in the Issue Council and activity in the PTU.
The Evocati Test Flight volunteer test program started in April 2016. Evocati are volunteers under a non-disclosure agreement. According to CIG their task is "playtesting builds to make sure they are stable before the build goes out to a wider audience."