Pascal was invented by Nicholas Wirth a long time ago to help teach programming.

Borland took Pascal and extended it to become Object Pascal by adding classes (and a whole heap of other stuff along the way).

Delphi was created by Borland as a rapid application development (RAD) environment that used the Object Pascal language. Through the various versions of Delphi, the Object Pascal was extended even further. Around the time of the release of Delphi 7, Borland officially changed the name of Object Pascal to Delphi. So now we have the IDE called Delphi and the language called Delphi.

FreePascal has also taken the basic Pascal language and enhanced it, usually following the same implementation that Borland used. FreePascal has differed in some small details, and has enhanced even further in other directions, but it does have a Delphi-compatible mode (-Mdelphi).