There's a difference between the two, but I think that a good Wall should be able to stall.
A wall is a pokemon that have high Defense/Sp. Defense and have good HP to pair with the defenses (aka Blissey)
A stall is a pokemon that have a move (or two) that slowly reduces the HP of the foe by either a status
affliction (Badly Poison) or a move that minimizes the damage the foe can put on you (Reflect) thus, slowly killing the foe without using attacks (aka Blissey - most Walls can be stallers too.)
