Pages data object. What does that mean?

At it says:

Each Go Template gets a data object. In Hugo, each template is passed a Page. In the below example, .Title is one of the elements accessible in that Page variable.

What data object is passed to what page? A template is a file containing Hugo templating commands (between {{...}} Ok. But what is a “data object”? In this context, what is a “Page”? The .Title is found in a somewhere? Where? How are things in layouts related to things in content?

I built a little site using Hugo back in August (going from the file dates.) Now I have come to modify it, and I am totally guzumpped by Hugo. I am totally lost. I cannot work out how to move content and restructure the site.

How should I get back into this? When I type “data object” into the search box at there is nothing I can interpret as helpful.