Work list web part icons

Hi All,

I've got a very basic question for which I can't find the answer. During one of the workshops at my current customer was asked which icons exist on the work list web part and the meaning of each of them. Underneath you can find a screenshot of 2 of them.

Can someone explain the meaning of these and/or provide the other icons/statuses?

Thanks in advance!

Kind regards,

Maarten