what is communism? and why is it failed?

While wondering in the world i have been encountered with many political agendas and political strategies but one thing that one of the highly discussed systems is Communism. I wanted to ask what is communism in simple words and why it is a system that is known to be failed.
While wondering in the world i have been encountered with many political agendas and political strategies but one thing that one of the highly discussed systems is Communism. I wanted to ask what is communism in simple words and why it is a system that is known to be failed.