What is split() in Salesforce?

Hiya, what context are you refering to?  Have you found it in some code?

I assume you are making reference to APEX code?  Ultimately it is used as a way to break a string/text value down into a list.

There is a good example on the Salesforce developer forums here, where the Ravindra provides an example of breaking an address down into its smaller components.

If you want to see the official documentation for the method, you can use the APEX Developer Guide (though if you are not a developer this link may be a little daunting): string method.split().

Hope that helps!