An algorithm is basically a set of instructions for solving a problem or completing a task. Algorithms normally start with an initial input and a set of instructions to calculate the output.
A search algorithm for example, is a procedure that determines what kind of information is retrieved from a database. Search algorithms use a query as the input and run it through a set of instructions to find the most relevant items to the query in a database.
On our site we often refer to the algorithms that Google and other search engines use to calculate the relevancy of user queries. These are the instructions the search engine uses for the SERP’s (Search Engine Results Pages) they present for user queries.
