Flood Check is a feature on Roblox which prevents Copy and Paste spams and bots. If you post a comment, you will have to wait a while (approx. 60 seconds) before you can post another comment.
On July 27th, 2017, a new 1 minute flood check was added to the forums instead of the old 15 second flood check, this was added along with the release of the Sub-Forum. This was heavily criticized by users on the Roblox forums, saying that the flood check is too long.
If you try to post a comment when you have flood check on the forums, it will show this message: 
"You are posting too fast. The flood check has blocked your post. Please press back and try again in a few seconds."
If you post comments too fast on other places like on a game, it will show this message in your text box instead:
"You are posting comments too fast. Wait a while until your next comment."
Flood Check Bypass
In December 2016, bots were constantly flooding game's/place's commentary section. How they bypassed the flood check is that all of the bots individually posted a scam instead of one spamming the commentary with it.
Almost all well-known present games were bombarded with bots, posting scams at least once a minute for each game. This resulted into the shutdown of the commentary, and no one can reactivate it for their place as comments are invisible and don't appear at the bottom.
Flood Check Hate Groups
Many groups have been made to fight flood check. One example is a group called Floodcheck is evil.