Electronic mail, or email, is a method of exchanging digital messages between people using digital devices such as computers and mobile phones.

Email first entered substantial use in the 1960s and by the mid-1970s had taken the form now recognized as email.

Email operates across computer networks, which today is primarily the Internet.

Some early email systems required the author and the recipient to both be online at the same time, in common with instant messaging.

Today's email systems are based on a store-and-forward model.

Email servers accept, forward, deliver, and store messages.

Neither the users nor their computers are required to be online simultaneously; they need to connect only briefly, typically to a mail server or a webmail interface, for as long as it takes to send or receive messages.

A telephone directory, also known as a telephone book, telephone address book, phone book, or the white/yellow pages, is a listing of telephone subscribers in a geographical area or subscribers to services provided by the organization that publishes the directory.

Its purpose is to allow the telephone number of a subscriber identified by name and address to be found.

A web search engine is a software system that is designed to search for information on the World Wide Web.

The search results are generally presented in a line of results often referred to as search engine results pages (SERPs).

The information may be a mix of web pages, images, and other types of files.

Some search engines also mine data available in databases or open directories.

Unlike web directories, which are maintained only by human editors, search engines also maintain real-time information by running an algorithm on a web crawler.

A landline telephone (also known as land line, land-line, main line, home phone, landline, fixed-line, and wireline) refers to a phone that uses a metal wire or fibre optic telephone line for transmission as distinguished from a mobile cellular line, which uses radio waves for transmission.

A background check or background investigation is the process of looking up and compiling criminal records, commercial records, and financial records of an individual or an organization.