This means essentially the same sort of thing as:
The tables are 10 feet apart.
That is, the distance between one table and the other table is 10 feet.
Another one:
Our birthdays are two months apart.
This means that the distance between your birthday and my birthday is two months.
If you were living in the year 2004, and I were living in the year
2006, we would be living two years apart. The distance between
you and me would be two years.
Of course, that's not possible in real life -- only in the movies!
CJ