Documentation: descriptions unclear about "inactive tabs"

[Chealer]

This extension's description on AMO reads:

"Auto Tab Discard" is a lightweight browser extension that automatically reduces the amount of memory used by open but inactive tabs, helping to conserve battery life on portable devices by disabling JavaScript code and DOM events on discarded tabs.

Its description on WebExtension.ORG reads:

The "Auto Tab Discard" extension is designed to automatically discard inactive tabs after a specified amount of time to reduce memory usage and prevent background scripts from consuming computational resources when it is not in use. This extension uses the native method for tab discarding, which means it does not suffer from the same issues as other extensions that use custom methods. When a tab is discarded by the native method, it is completely removed from memory and does not use any resources, but it can be restored to its previous state, including preserving page state such as scroll position. The extension also allows you to configure an exception list and specify types of tabs that should not be discarded, such as pinned tabs or tabs that are playing media.

Its description in its README file reads:

Auto Tab Discard

A browser extension which uses the native tab discarding method (chrome.tabs.discard) to automatically reduce memory usage of inactive tabs. This extension is more efficient and should be less buggy compared to the alternatives extensions that use DOM replacement method.

Clearly, the concept of tab activity is central in defining this extension. But unfortunately, it is not defined.

Please clarify which tabs are inactive.