What is the difference between organic search results and paid search results?

Search Engine Optimization (SEO)-Organic Search Results

Search engine optimization is commonly referred to as the process of improving the volume or quality of traffic to a website from search engines through the use of "Natural" or organic un-paid search results as opposed to paid inclusion.

Pay-Per-Click (PPC)-Paid Search Results

Pay-Per-Click (PPC) is an advertising model used on search engines, advertising networks, and content websites or blogs, where advertisers only pay when a user actually clicks on an ad to visit the advertiser's website.  Advertisers bid on keywords that they believe their customers are using to find their products or services.  When a user types a keyword matching the advertiser's keyword list, or views a page with relevant content, the advertiser's ad may be shown.