SEO = Search Engine Optimisation
SEO refers to the processes carried out with the objective of making a website appear higher up the rankings on search engines such as Google and Bing. Broadly speaking, it refers to four types of activity:
Generally SEO refers to increasing your ranking in the unpaid search results. The term SEM (search engine marketing) includes paid for search results such as Google Adwords.
SEO Companies charge a fee for advice and for carrying out SEO activities. They may charge an agreed fee for a set of activities or they may charge for work by the hour to an agreed limited. They may be paid based on results although they can be hesitant to do so, and this can lead to black hat SEO.
Black hat SEO refers to SEO methods which may radically increase a websites search rankings in the short term (during which time the SEO Company may be paid) but in the long term may lead to the website being banned from the search engine. They include methods such as: