An alternate, and I'm told characteristically North American use of the word truffle is in description of a particular kind of chocolate.
If you go to any reputable chocolatier and look in their display case, you will likely see several trays of small round chocolates, about 10% smaller than a ping pong ball. To be a real truffle, the chocolate must have a flavoured center which is often another type of chocolate, or a liquer-flavoured nougat. Because of the incredible diversity of possible fillings, the truffles are usually marked externally through the use of different colours of chocolate, and sometimes through coloured or patterned icing on the top of the truffle.
Truffles are considered by many to be the pinnacle of chocolate (much as, and perhaps in direct reference to, the fungal truffles are acknowledged as one of the best delicacies, and certainly the best fungus) and are an excellent way to impress your significant other - if he/she/it is into chocolate in the slightest.
If you are a truffle virgin seeking guidance in the selection of your first truffle - go with simplicity. If you have a favourite liquer, the truffle with that filling is likely going to be pleasing, irish cream truffles being excellent, for example. Another one that's generally appreciated is the champagne truffle, which lacks the acidity of actual champagne, but retains the light taste. And of course, to play it really safe, get a milk-chocolate truffle, which is just chocolate-on-chocolate, but which has an excellent texture and flavour nonetheless.