There are 10 different types of Anomaly Class ranging from Class 1 (easiest) to Class 10 (hardest).

Class 1 = (Faction) Hideaway or Drone Cluster (easiest)
Class 2 = (Faction) Burrow or Drone Collection
Class 3 = (Faction) Refuge or Drone Assembly
Class 4 = (Faction) Den or Drone Gathering
Class 5 = (Faction) Yard or Drone Surveillance
Class 6 = (Faction) Rally Point or Drone Menagerie
Class 7 = (Faction) Port or Drone Herd
Class 8 = (Faction) Hub or Drone Squad
Class 9 = (Faction) Haven or Drone Patrol
Class 10 = (Faction) Sanctum or Drone Horde (hardest)

Each Anomaly Class has 4 different level's ranging from Level 1 (easiest) to Level 4 (hardest).

Level 1 = (Faction name) + Anomaly Class (easiest)
Level 2 = (Faction name) Hidden + Anomaly Class
Level 3 = (Faction name) Forsaken + Anomaly Class
Level 4 = (Faction name) Forlorn + Anomaly Class (hardest)