A misaligned die is when the hammer die is off alignment in orientation to the coining chamber and when it strikes the coin the obverse side of the coin is struck off center. The misaligned strike is only off center on one side of the coin, if both are then it is called an off center strike. Also misaligned strikes can result in partial collar strikes as well.
The 1981-P Jefferson Nickel Misaligned Die in the above image sold for $258.50 but value was dependent on the grade of MS66 and the fact that it was well struck with full steps on the reverse Monticello. Otherwise it would have sold for $30 to $60. Value is also dependent on how far off a coin is struck misaligned as well. Value will also depend on the rarity of the date and mint and if the coin is modern or type coin.