Automatic indexing involves creating a list of key terms for a document to help with finding information. There are two main ways to do this: by looking at the words in the text or by using a pre-defined list of terms. Evaluating automatic indexing is tricky, but it's usually done by seeing how well the index helps with finding information in a text. Lately, automatic indexing has been used for tasks like sorting texts into categories. In the future, indexing on the web will be a big challenge.