What Does Google Define as Spamming?

Hello,

I have a website that I'm trying to maximize so that it will rank as highly
as possible for its keywords on Google.

I plan to have several pages with *almost* identical content, under the same
domain, so that the pages will be listed one after another on Google. In so
doing, I hope to increase my chances of capturing traffic.

To what extent can I have pages with almost identical content before it's
considered spamming by Google, thus risking having my domain banned?

Thanks!

David