A wide range of software asks for Club Log credentials as part of real time uploads, or other low level connections to do with log matching (e.g. RSGB IOTA matching, DARC awards, WIA awards and probably others, too). It would obviously be better not to have to share your password in this way as it could end up being mishandled or accidentally compromised.
Club Log offers "Application Passwords" to help you provide access to those tools, while also keeping your personal password private. Application Passwords are valid in combination with your username (your email address), but they only work with the API, and don't provide access to Club Log via the main web site. You should use Application Passwords rather than your real password in order to safe-guard your password details.
Application Passwords can be created or deleted from the Settings > App Passwords menu.