What does the Envelope Colors besides the threads mean?

Hello IndusLady, Could you please help me understand what the envelope colors mean. I have attached a picture for reference. When I open a list of threads, they have envelopes on the left in various colors, sometimes open and sometimes closed.
I could not find a note anywhere in my search on what these mean.

Also, sorry for posting my query here. I was not able to open a new thread, maybe because I am new here and haven't completed 50 posts yet.

Thank you,
Sarita.

Hi Saritaji,

If you scroll all the way down in the same page where you see the thread listing with these envelopes, you will be able to find a legend about the envelope colors.

They are:

New posts
Hot thread with new posts
No new posts
Hot thread with no new posts
Thread is closed
You have posted in this thread

PS: FAQ forum does not allow any member to start new threads. However, you can post your queries (that is not already addressed in this forum) here - Ask Questions To IndusLady about IL FORUMS