Terminal and shell are two very different concepts, though the separation is not obvious to the uninitiated (and the exact location of the separation is a little strange).
- The terminal mainly provides a way to type and display characters.
- The shell mainly provides a way to execute commands.
I recommend using terminal only for questions that are related to the terminal (emulator) and its configuration. Using this tag for “how do I do X on the command line” feels wholly counter-intuitive to me. I recommend keeping a separate command-line for this purpose.
The command-line tag should be used for questions that ask if or how something is done using the command-line as opposed to the GUI. The terminal tag is concerned with questions about the terminal iself, that is what you see when you press Ctrl+Alt+F1. When the question is specific to gnome-terminal or konsole, these tags should be used instead.
There is no meaningful distinction between the command-line and the terminal to be made by normal users, the tags should be merged. This will make it easier for users to search and tag their questions, and it won't impact the quality of answers.