This means that the bundle mentioned has a dependency which will no longer be available when you upgrade to 6.5, so it won't work anymore.
The screenshot is very small but if I'm not mistaken you got this warning for a bundle that is part ACS Commons, correct? What version are you using?
If you look at the compatibility matrix, you will see that you need to be on version 4.x.x minimum for AEM 6.5 (which is also compatible with AEM 6.3). If you update ACS Commons to 4.5.0, the issue should be fixed 🙂