Put simply, what it means is that rather than fully left-aligning an element with the grid, some padding is required so that the element is nudged away from the grid-line a little
“ The grid system is an aid, not a guarantee.
It permits a number of possible uses and each
designer can look for a solution appropriate to his
personal style. But one must learn how to use the
grid; it is an art that requires practice. ”
The ultimate resource
in grid systems.