Any electronics-related web page that uses "shield" other than as meaning "RF emission/reception blocking element" is automatically obnoxious, mobile or not.
it is a very common and well known term in the Arduino world, and the physical appearance of the device with all of the header pins would immediately suggest shield applications to anyone who has spent time with Arduino
"Card" is two characters less than "shield", and has a long history in computing denoting a circuit board that is plugged into another circuit board. (Whereas "daughter" is usually not redundant in "daughterboard", it can almost always be dropped from "daughtercard".)
Examples: network card; disk controller card; video card; SD card.
"Shield" is such an entrenched term in electronics, from long before computing, that it's completely stupid to try give it another meaning. It's also not from some specialized sub-domain whose rare terminology can be reused; shielding is employed in all kinds of devices.