PPC stands for pay per click and it is method where visit is purchased or per click is paid. It is generally done to increase the traffic to your site.
ppc stands for pay per click, cpc stands for cost per click. It is a type of purchased visit where you pay for each click or visit to your site. This can be seen in search engine advertisement.
SEO stands for search engine optimization, in this we improve the position of the ranking on search engines. It is also responsible for the traffic to your site.