Search engine optimization is the process of affecting the online visibility of a website or a web page in a web search engine’s unpaid results–often referred to as “natural”, “organic”, or “earned” results.
Traffic coming from good ranking in organic search results needs no further promotion, other than continuing to produce content that users want to see. SEO may target different kinds of search, including image search, local search (such as NYC SEO), video search, academic research, news search and industry-specific vertical search engines.
Once known as “search engine optimization”, SEO can also be called “online marketing“, especially when it relates to increasing traffic to a business’ online presence. Some refer to SEM as “search engine marketing”. For this reason, SEO is sometimes considered to be part of SEM (“search engine marketing”).
The difference between SEO and SEM is ambiguous, so they are often described as being the same thing.