They are an evolution of the second-generation programming languages. In short : 3GL. The third generation tend to make the languages more programmer-friendly. This includes features like improved support for aggregate data types, and expressing concepts in a way that favours the programmer, not the computer.
A third generation language improves over a second generation language by having the computer take care of non-essential details, not the programmer. "High level language" is a synonym for third-generation programming language.
First introduced in the late 1950s, Fortran, ALGOL, and COBOL are early examples of this sort of language. Most popular languages today, such as C, C++, C#, Java, BASIC and Delphi, are also third-generation languages.
Most 3GLs support structured programming.
