What is a tank?

Today we'll be going over the different classes and sub classes of Tank. Though a bit late here it is. Thank you much for watching and enjoy.
The footage of the Type 97s are from here: https://www.youtube.com/watch?v=aVSWRtNt680
The footage of the Churchills are from here: https://www.youtube.com/watch?v=te-dwC2IqF4
The footage of the Bradlys is from here: https://www.youtube.com/watch?v=3Vmikwrhc5E
The footage of the BMP-1is from here: https://www.youtube.com/watch?v=txAYJFpozb0