The document provides an introduction to transfer learning in natural language processing (NLP), explaining its relevance and significance, especially through examples like ULMFiT, ELMo, and Glomo. It discusses the evolution and impact of transfer learning methodologies, particularly the transformer architecture from Google, which has become foundational in modern NLP. Additionally, it highlights the differences in training and test distributions as well as the variety of text types and characteristics that affect NLP tasks.