A personal access token is a string of characters that functions similarly to an OAuth token in that you can specify its permissions via scopes. A personal access token is also similar to a password, but you can have many of them and you can revoke access to each one at any time.
As an example, you can enable a personal access token to write to your repositories. If then you run a cURL command or write a script that creates an issue in your repository, you would pass the personal access token to authenticate. You can store the personal access token as an environment variable to avoid typing it every time you use it.