A Pay Per Click network offers a number of opportunities to get your ads in front of potential customers. The Search network refers to ads showing within the results listed on a search engine. These are usually placed at the top and to the right of the organic (free) result listings. Search can also include Search Partners, websites that use a search engine's services within their website, e.g. site search.
The Display network includes partnered websites that will display ads on any or all of their web pages. These websites vary by industry, but will usually earn revenue from this partnership. Sometimes, instead of doing a PPC model, the advertiser will opt for CPM or Cost Per Thousand Impressions. This is done when click-thrus aren't desired and visually use banner ads as a way to optimize for brand recognition.