 What is ELMO, a stack of transformer encoders, a stack of transformer decoders, a stack of unidirectional LSTM cells, or a stack of bidirectional LSTM cells? I'll give you a sec. The correct answer is D, a stack of bidirectional LSTM cells. ELMO, or embeddings from language models, is a language model introduced in 2018 that attempts to create high-quality word embeddings to truly understand words. Follow for more on NLP.