Latent semantic analysis (LSA) is a statistical technique used to uncover relationships between words and documents. It can be used to determine the most relevant words for a document, to find similar documents, and for document summarization.

Topic modelling is a technique used to find and extract the main topics from a collection of documents. It can be used to find relationships between documents and discover clusters of documents about similar topics.
What is the difference between latent semantic analysis and topic modeling?