Definition: Is the data accurate? For example, let's say we've received a dataset of fingerspelling videos. We check the dataset by looking at the videos, looking at a video that supposedly fingerspell my name "Ben" and seeing that the fingerspelling was done with wrong handshapes and positions. We realise that this dataset is not accurate. So we discard this dataset. We look at a different dataset, find one where my name is fingerspelt with the right handshapes and positions, and so it is accurate.