Columns sound no good

Created by: Chealer

The documentation's first section on the Grid system asks "Sounds good?". It is hard to answer, but it sounds vague.

The whole section brings more questions than it answers, but one particularly problematic part is the item

Content should be placed within columns, and only columns may be immediate children of rows.

At this point, the meaning of "column" has not been defined, and I do not see it defined later neither.