What does it mean On-page Optimization ??

[PK357]

Those are all valid answers. However, you should always start with an on-page checklist. These are any factors within your control, and are accessible with front end CMS access.

This includes:
keywords
meta descriptions (less than 160 characters)
title tags (less than 70 characters)
on page content
alt tags for images on site
canonical tags for URL's
Proper URL structure - nothing overly long and complex
good pagination - if you have a blog make sure posts don't all render as one page. if you prefer the scroll look, limit the number of post thumbnails to 8-10 per page.
XML sitemap
proper interlinking
bold or emphasis tags <strong></strong>
privacy policy/about/copyright inclusion
google analytics code in header not footer
usability testing
elimination of 404 errors
proper configuration of robots.txt file to deindex sensitive admin pages
proper use of header <h1><h2> tags
keyword density checking
proper code rendering - no flash (or will exclude iPhones etc)
no sloppy code -- also known as code bloat which slows pages down.
competitive analysis.

There are other items, but if you do all of these things, you will set yourself up for success eventually.