What is 'independent assortment'?
The term was pioneered by Mendel, who had no knowledge of chromosomes, so definition 1 would perhaps be the best answer. However, we now know that definition 1 arises from definition 2 (chromosomes are inherited independently of each other) and from the fact that chromosomes recombine (cross-over). 

That said, independent assortment does not apply to linked genes, which tend to be inherited together. That is, they are not independently assorted.