Padding is a term used in cascading style sheet (CSS). The padding specifies the amount of space, in px, between an element and its content.
Pagejacking is stealing a web page’s source code for later re-publishing it. Pagejacking is a form of Black hat seo. Sites doing pagejacking are penalized by Google and often see their ranking and traffic decrease. They also encounter the risk of being unindexed by the search engine.
A pop-up is a new window which usually opens as a result of an action undertaken by a user. For example clicking on a link.
Pop-ups are usually treated as spams. Many new browsers include pop-up blockers.
PPC or Pay per click is an online marketing strategy whereby the advertiser pays for the number of times users click on the advertisement. The amount of clicks is usually bought or agreed on beforehand.
A plug-in is an standalone application usually built into browsers to enable the browser to open or view files of a particular format. For example .pdf files, movie files etc…