A programming language with a specific domain intended, such as business or science, in which the basic units are of a higher abstraction or power.
Following on the heels of 3GL languages such as C, COBOL and Pascal, the promise of the 4GL was to solve the problem at a higher level of abstraction. A 4GL would be designed with a specific problem domain in mind, such as commerce.
Many 4GLs did not go on to fulfill their initial promise, as 3GLs continued to expand in power and scope, and standardized libraries became more pervasive. The line today between a 3GL and a 4GL is blurry; most modern languages could be considered 4GLs.
Simply tagging your post 4gl should be avoided. It's better to tag your post with a tag of your specific 4GL-language. Or at least add the language tag to the 4GL-tag.
Examples:
Informix 4gl can be tagged informix.
Progress 4GL/ABL --> progress-4gl
Ingres --> ingres
etc.
