Differences between eCommerce and Web Channel

Hi. I'm really new to SAP. I'm looking at leveraging some of the built-in e-commerce functionality of SAP. I've read a few articles on the SAP help site but I can't distinguish the differences between the following 2 solution options:

1) ERP eCommerce

2) CRM Web Channel

From what I've read, both of the above technologies do relatively the same thing. Can someone let me know if this is true, or if not, where I can find details on when to use one versus the other?

Thanks!

- Dylan