Explanation of Settings > Apps and internal vs external storage (Android 4.1)

Question

Can anyone please provide a clear explanation of the different information displayed in the Apps section of Android Settigs? Precisely:

Apps List

1. The ON SD CARD tab. Does it show apps that are installed on the SD card, or any app that has some data stored on the external storage, even though the app itself may be installed internally?

2. The checkboxes. Does it indicate that this app is actually installed on the external storage? Implying that the unchecked apps are installed internally, but have some data stored on the SD card?

3. The size in MB. Is this the total amount of data this app has stored on the SD card, including the app "executable" itself, in case the app is also installed on external storage?

App Details

4. The 'Move' button. It offers either a) Move to Internal Storage or b) Move to Data Storage. Is this a reliable indication of where the app is currently installed? I.E. when it offers to Move to Internal Storage, is it safe to assume that the app is installed on external? Or does it say nothing about where the app executable is located, and is only offering me to move any app-related files to the internal memory? Is data storage synonymous to external storage ?
5. What do the different sizes mean? I mean App, USB storage app, Data, SD card.

Thanks in advance to anyone who takes their time to try and clarify this to me!