Client Libraries in Selenium

The client libraries provide the programming support that allows you to run Selenium commands from a program of your own design. There is a different client library for each supported language. A Selenium client library provides a programming interface (API), i.e., a set of functions, which run Selenium commands from your own program. Within each interface, there is a programming function that supports each Selenese command.

The client library takes a Selenese command and passes it to the Selenium Server for processing a specific action or test against the application under test (AUT). The client library also receives the result of that command and passes it back to your program. Your program can receive the result and store it into a program variable and reporting it as a success or failure, or possibly taking corrective action if it was an unexpected error.

So to create a test program, you simply write a program that runs a set of Selenium commands using a client library API. And, optionally, if you already have a Selenese test script created in the Selenium-IDE, you can generate the Selenium-RC code. The Selenium-IDE can translate (using its Export menu item) its Selenium commands into a client-driver’s API function calls. See the Selenium-IDE chapter for specifics on exporting RC code from Selenium-IDE.

Imp Question--- "The RC server also bundles Selenium Core, and automatically loads it into the browser."
Selenium Core (Core) is a DHTML test execution framework.

It is the engine of both, Selenium IDE and Selenium RC (driven mode), but it also can be deployed on the desired application server.