Card Boarded refers to cards like these as "Goaltending Gallimaufry". Basically, they are cards which feature goaltenders where the equipment doesn't match the uniform, as seen in trade or call-up situations. Sometimes, they even morph into nicknames for the player, as when Johan Hedberg debuted in Pittsburgh after a trade, then call-up from the Manitoba Moose.
For the purposes there, it can be any part of the equipment, including the pads. However, I'm just interested in the masks. Surely, I've got 3 of those for a masked Monday? Yup. I've got at least 3, but these were the first I came across.
Johan Holmqvist in Dallas, but still sporting Tampa Lightning coloured pads. Here's the other goalie part of the trade, with Mike Smith still sporting his Garth Brooks mask from Dallas while in a Tampa uniform.