The 1st dimension (1D) is like a line, or another way to put it, absolutely nothing but length. When something is termed 1dimensional it does not do anything, but simply is, and stays that way. Pong control (the control, mind you, not the game) is 1D along with Morse code.
The second dimension (2D) is like a flat plane. The term width is added here. A object can exist up, down, right or left into infinity. This is handy for simple pictures, writing, and a bunch of old 80's arcade games. This paper/screen could be called 2 dimensional (although this is utterly false)
The third dimension (3D) is like a box. The term depth, is used a lot here. Here not only can an object exist up, down, right, and left, but can now exist towards, and away from you. Fully 3D objects can exist here, YOU are existing in the 3rd dimension right now in fact. Computer games, pictures, and graphics said to be 3D are sadly mistaken, unless you read this entire thing. The concept of 3 dimensions can be displayed on a 2 dimensional screen/paper/rock, and even the illusion of 3 dimensions can be shown here, but it is all still 2D. This is all probably an absurdly obvious fact to most of you but this just makes it all clear.
The fourth dimension (4D) is time, imagine a box moving upon itself, or better yet, through time. No real specific term is assigned to this but When might work. As a 3D object exists, it can move, (duh) but it has to move into the 4th dimension, because itself is still occupying the space it moved from. For example: a 2" cube (3D) tries to move 1 inch left, presuming it doesn't move in time, then it runs into the 1/2 of itself still existing from whence it came. (DO NOT try to show me this as an experiment, seeing as you can't, because WE ARE ALL 4TH DIMENSIONAL BEINGS.)
SO a moving 3D object is traveling in the 4th. THEREFORE a 2D object moves in the 3rd and a 1D object moves in the 2nd and a 0th presumably travels in the 1st. Existing and moving are quite different things. ALSO, We are all moving at a relatively similar speed to everything else on this planet. (although atomic timepieces show that time does, in fact, move faster on top of mountains) SOOOOOOOO: considering that we are all constantly moving in this respect and I've yet to see someone suddenly stop in time, I conclude that we are all, in fact, 4th dimensional beings in a 4th dimensional universe who haven't gotten the knack of controlling their time travel. This also means that the computer game manufactures and marketers were right, their games are in fact 3D, a 2 dimensional picture with objects in it that move. Pong was also a 3D game. LONG LIVE PONG!!
More about Time Travel and such