What is the meaning of Tasks and Running in htop screen?

Tasks do represent the number of opened processes. (Note that I do not use the term "running" to avoid confusion.)

You have to realize that not all opened processes consume CPU constantly.

Each process can be in a number of different states:

• running: actively using CPU
• stopped: the process was stopped (paused) by the user
• defunc or zombie: process is actually blocking on an external resource, commonly a disk drive
• sleeping: most common state as many processes actually sleep a lot of the time and do small checks at different intervals, or wait for user input