Apps are native applications developed on some programming language, specific to the device (Ios, Android, etc). Some apps are not fully "apps" and will just load a url.
Jquery is the mobile version of Jquery, optimized for mobile and being lightweight.
Fluid layouts adapt to the screen size depending on the screen resolution, via CSS and sometimes using JS.
This might be of your interest: [webmasterworld.com...]
As for the online shop well I'm on the same crossroad. I made my websites mobile enabled but still wondering on the shopping cart thing.