Writing: What is the "argument"?

When I was reading about how to improve my thesis writing, I often saw things like:

• be clear about your argument
• delete whatever doesn't address your argument
• add signposts around your argument
• you should design the structure of your paper around your argument

... but I was always like: "WTF is the argument?"  I knew what my thesis statement was:  It was the last sentence of my first paragraph.  It was the main point of the paper in a single sentence.  But what was my argument?

Finally, I came across this beautiful explanation in Bad Choices by Ali Almossawi:  "An argument is made up of a set of statements known as propositions, each of which may be true or false."

Ah, ha!  OK!   So if my thesis statement is like a question, then my argument is the fleshed out answer.  It is a set of propositions (facts), each of which I would explain and elaborate on and relate to what others have said.  I get it!!!