Natural language (NL) is just human language, for example English. This is in contrast to programming languages like Java. When people talk about “NL” aspects of Cyc, they are referring to Cyc’s Natural Language Processing (NLP) which includes both Cyc’s ability to generate natural language from CycL (i.e. Natural Language Generation (NLG)) and Cyc’s growing ability to understand natural language (i.e. Natural Language Understanding (NLU)).