Offline learning refers to using a static dataset for your learning algorithm, while online learning means that you are operating on an ever growing dataset and learning occurs as the data becomes available. 
If you were to train a comment filter, for example, you could either get a dataset of inappropriate comments an train on the entire set (that would be offline learning), or you could update the dataset as you find more inappropriate comments and train the filter on the new data (that would be online learning).
spam fails_task lang_mismatch pii not_appropriate hate_speech sexual_content quality toxicity humor helpfulness creativity violence