Corked wine, or cork taint is a fault that afflicts wine, and despite popular belief has nothing to do with bits of cork floating in your glass. Cork taint can be caused by a heap of factors not just the cork  including wooden barrels, storage conditions. But the poor cork is generally held to be spoiler of wine.  An important thing to note is that cork taint can affect wines irrespective of price and quality level.

Now the sciencey bit, cork taint is caused by 2,4,6-trichloroanisole (TCA) in the wine.  Corked wine with TCA has a nasty  non winey smells like moldy paper, wet dog, damp cloth or carpet. And the flavours in the mouth are just unappealing and disgusting!

Improvements in cork and winemaking mean lower numbers of bottles with cork taint.  Screw caps and synthetic corks  have also helped in lowering the amount of bottles with TCA.