For Eg: if Nomad 7/8
BF Lord 7/8
or LN FFA 7/8

Each game room has 8 spots for 8 players, and the first number will show you, how many players have already joined. When the host of the games adds this to their game description, it probably means, that they will launch at 7 or 8 players and that they are willing to even play only 3v3 in case someone dropped. This is very specific to RM / CS etc.

thank you very much but I didn't get two of your points.
1) If one leaves it will 7/8 is it what you meant to say?
2) or If host can see 7 other players and the room is meant for such 7 players but not 6 such players or 8 is impossible as the room size cannot go to 9, but why didn't you mention whether the host wants 5/7 because 5 players is enough for 3v3

Thy just write 7/8 in name of room because they hope that you think there is only 1 free place anymore and they need only 1 player anymore so game will start quickly...

I NEVER join those rooms because I hate this...

Also good to know, last time I saw people doing this was more than 20 years ago.