Is Tetris a packing or covering problem? I am looking for some information about packing and covering problems. Some texts mention Tetris without further elaboration. Now, I am wondering if Tetris is a kind of packing or covering problem.
According to Wikipedia,

packing : '... involve attempting to pack objects together into
  containers'
covering : '... how many of the same objects are required to
  completely cover every region of the container'

Let us consider the situation that given $n$ tetrominoes, we opt to find as many gap-free rows as possible. (Thanks @Newb for pointing this out.) On one hand, when playing Tetris, I would like to pack the tetrominoes as densely as possible so that no holes appear in a row. On the other hand, we are covering the rectangular 'board' with tetrominoes. Which interpretation is correct?
I would also like to take this opportunity to ask for reference for packing and covering problems for those who are new to this area. Any help would be appreciated.
 A: I think this is not a packing problem. Packing problems are usually in the context of geometry -- how many hexagons can I pack in this circle? How many tetrahedra can I pack in this sphere? i.e. usually involve continuous areas/volumes. 
Tetris, on the other hand, is totally discrete: one block per square! There's no area/volume manoeuvring to be done here. In fact, we can represent the Tetris game as a graph with $200$ nodes (the Tetris board traditionally has dimensions $20 \times 10$). When we view the board like this, then I think this is reasonably close to the class of graph covering problems. 
It may not be a covering problem in the traditional sense (we usually talk about minimal vertex covers), but it's definitely close enough to call your problem a covering problem, rather than a packing problem.
(By the way, to further convince yourself, I suggest reading the introduction of this Wikipedia article on packing. The 'container' in your problem is very much unlike the containers of traditional packing problems.)
