When you deactivate a WordPress plugin, it is simply turned off. However, it is still installed on your website, so you can activate it again if you need to. On the other hand, uninstalling a plugin completely deletes it from your website. You will not be able to see the plugin on the Plugins » Installed Plugins page

In some case, you have to do this, in order to find where is the bug.

You activate then, one by one, and you may see which plugin has the problem.