Keyword - A word people text in order to receive an auto-response, join a list, and trigger other workflow steps. For example, you might create a keyword, Text CONNECT to (775) 347-7333. You can have multiple keywords for different ministries, events, sign ups, etc. You are not limited to using just one keyword at a time.
Lists - Where your subscribers (contacts) are stored. Each keyword you create can be tied to one or more lists. You can have as many lists as you'd like, and subscribers can be in multiple lists simultaneously. People can join a list through a Keyword, but they can also join through other ways like importing a CSV file or integrating with your Church management software.
Note: if you delete a Keyword, you will not lose the list that it's tied to. You will still have that list and any subscribers in it.