Sequence-to-Sequence (Seq2Seq) models are a class of models used in Natural Language Processing (NLP) to generate one sequence of text given another sequence. They are widely used for tasks such as machine translation, text summarization, and question answering. Seq2Seq models consist of an encoder and a decoder network. The encoder processes the input sequence and transforms it into a fixed-length representation called the context vector. The decoder then generates the output sequence based on this context vector.