Likely.js is a library used for collaborative filtering and making recommendations. It takes an input training matrix where the rows represent users and the columns represent items. Each entry in the matrix is the rating the user has given to that item. After training, you can retrieve a list of recommended items and their estimated ratings for any given user. For example, you may provide as input a training matrix where each row is a customer and the columns are the ratings they give to various movies. Then you might use this model to get recommendations for movies a given customer might like that they have not yet seen.