Source : Free On-Line Dictionary of Computing

logical shift
     
         (Either shift left logical or shift right
        logical) Machine-level operations available on nearly all
        processors which move each bit in a word one or more bit
        positions in the given direction.  A left shift moves the bits
        to more significant positions (like multiplying by two), a
        right shift moves them to less significant positions (like
        dividing by two).  The comparison with multiplication and
        division breaks down in certain circumstances - a logical
        shift may discard bits that are shifted off either end of the
        word and does not preserve the sign of the word (positive or
        negative).
     
        Logical shift is approriate when treating the word as a {bit
        string} or a sequence of {bit fields}, whereas {arithmetic
        shift} is appropriate when treating it as a binary number.
        The word to be shifted is usually stored in a {register}, or
        possibly in memory.
     
        (1996-07-02)