to "bank" is to hit the ball off a wall when you shoot...like using a bumper in pool. Most common is from goalie position (the 2 bar) and then some from the forward position (3 bar). Some tables are built in such a way that they are easier to bank on than other tables and that is what comes up from time to time in this forum. Tornado, the table most used in the US for competition, has never been very good for for banking (so say the vast majority of people although there are one or two that say otherwise)...many of us though have played on tables where you could bank with skill and those of us who play on Tornado miss it.
As I explained in another thread, any table with lowered feet, Tornado, Shelti, Warrior or other table, where the bottom of the feet are lower than the midpoint of the ball, will make banking less effective, due to the physics.
The allowable area for a banked ball at or near the floor (skipping) is definitely decreased, because a ball has to clear a Tornado player's feet with no tolerance! You cannot fit from the side any ball underneath the player unless the player's at a very high angle!
With narrower feet (Dynamo, TS, Garlando, Bonzini, P4P, etc..) and being further from the floor, the ball has extra area and clearance to go almost 1/6 under a player! You can shoot great bank shots on a Tornado or similarly footed table, but you have less open area under the 3bar, 2bar and especially the 5bar to get through. Do the math. Imagine an area under the 5bar spanning the width of the table, and the height of the foosball. The clearance with the players (straight down especially - hint to those defending banking insane maniac goalkeepers) is a lot less under Tornado and similar players than the old Dynamo or TS players, especially with the wider squared off Tornado feet.
That's also why good zones work even more effectively on Tornado and similarly footed tables! The best dead-on bankers and those who have 3-4 options will still get banks through, but it certainly is harder. And the more practice and hours it needs to learn pinpoint banking, not to mention the adjustment to having to make sure you hit above the midpoint or right on it.
Improving players will naturally see more improvement with "straight through" shots much more quickly. So of course the goalkeepers will concentrate on basic shots with the stiffer and more reliable Tornado-type players, not to mention passing to the forward, where the larger goal and the dominance of today's rollovers and pull shots makes the advantage that of clearing for a higher percentage to the forward.
The only effective and most common bank I have seen employed on tables like Tornado is the 5bar bank to the near goal corner. A shorter distance, with less skipping to get fouled up by one of the outer goalkeeper rods, once the the 5bar has been cleared. The goalkeeper's 2bar players are also naturally set to prevent the straight-in shot, forcing the other 2bar player way out of the bank line. Alas, most defenders get repulsed by it because they believe most of them are inadvertent and "slop". This can be seen with mis-hits when doing an off-the-wall brush down from the near or far 5bar player, which can turn easily into a bank into the near goal corner. Ever seen that? Sound familiar?