What is Conclave?
Conclave is the PvP gamemode within the game Warframe.
What is RC / NonRC?
RC stands for 'Recruit Conditioning'. This is intended to be a mode for newer players where they can be matched with others of a similar skill level. When viewing the Conclave terminal in your ship, you will see a checkbox near the bottom right to toggle this on and off (where in terms of this site, RC is when it's on, and NonRC is when it's off). You are able to toggle this on/off until you reach rank 3 in the Conclave syndicate, at which point it is permanently locked off (i.e. NonRC mode).
By default, this mode is enabled unless you either turn it off or reach rank 3. If you are just starting out with Conclave, it is recommended to leave this enabled.
What are these game modes?
The game modes listed on the site may be slightly different than what appears in-game for design / spacing reasons, and also to align with what they're commonly known as in the community. The game modes are:
CTF - Capture the Flag (Cephalon Capture)
FFA - Free for All (Annihilation)
Lunaro - Lunaro
TA - Team Annihilation
Why do I repeatedly experience host migrations?
In most circumstances, you are probably using a weapon that has been marked as a banned weapon. These are items or warframes that are bugged due to years of neglect on DE's part, and they have either become incredibly overpowered damage-wise, or are just flat out broken with serious unintended side effects.
Whenever you get a kill with an item that is banned (or a kill using a Warframe's ability, if the item itself is a Warframe), you will be kicked and temporarily banned (typically 5 minutes) from connecting to that server again.
The bans may differ per server, and can be viewed
here