Scraping refers to using a computer to retrieve the code of a webpage. Once the code is obtained, it must be parsed into a useful form for further use in R.
Base R does not have many of the tools required for these processes, so scraping and parsing are typically done with packages. Some packages are most useful for scraping (
RCurl), some for parsing (
xml2), and some for both (
A related process is scraping a web API, which unlike a webpage returns data intended to be machine-readable. Many of the same packages are used for both.