How To add a shortcut key to the terminal in LXDE?

Key bindings come mostly from desktop environment, although linux distributions may set some "default" in config files.

You can point to "LX terminal" by the name of its program which is called lxterminal. For example inside LX terminal you can write 'lxterminal' to run another instance/window of terminal.

If you use LXDE, open box, and you want to bind ctrl+alt+t to open the LXTerminal, you need to add

<!-- Launch LXTerminal with Ctrl+Alt+t-->
    <keybind key="C-A-t">
      <action name="Execute">
        <command>lxterminal</command>
      </action>
    </keybind>

to ~/.config/openbox/lxde-rc.xml.

Key bindings are found in the <keyboard> section of your rc.xml configuration file. Any bindings outside of that section are not valid and will be ignored.