Natural Language Generation (NLG) and Natural Language Understanding (NLU) are sub-parts of natural language processing. Natural language understanding interprets the input text with the representation it has in the expert system and then understands the meaning of the sentence, whether written text or speech. Natural language generation maps the internal model to logical interpretation and displays the output text or speech. It generates the natural language using machines. Natural Language Understanding is the process of interpretation and reading of the language, whereas natural language generation is the process of writing and generation of the logical text.