Normal tile is a tile seen in Run 1 and Run 3. It is the most basic type of tile. The ones in Run 2 is not counted as this type of Normal tile, since they are more similar to that of a Box than a tile in terms of width.
Normal tiles appear in Run 1 in Run 3. In Run 1, normal tiles are one of the only two tiles to appear, the other one being holes (Well, unless you count bouncy tiles, but those are only in the level editor). They appear in almost every level in Run 3, but there are some exceptions, such as some Winter Games levels (Well, the transition from level to level is made out of normal tiles, but that doesn't count). Normal tiles appear in many different colors. Most levels are only one color, but there are some multicolored levels in the New Tunnel and Not the Way Back, those 'multi-color' tiles just brighter in color than the other type of tile in the level. Also, normal tiles can be in any color. (Even black, but that's in the level editor and IM Level 268 only.)
This tile is just a regular tile, absolutely nothing special. When you step on it, you just walk on it, nothing else happens. Even though this tile is two-dimensional, if you hit the edge, the tile will bump you in a certain way, based on how you hit the tile. Otherwise, you will just run on top of the tile. If you hit one of these tiles on the wall, you will change gravity so that tile becomes the floor.
There are some interesting exceptions to standard gameplay mechanics. One is that if you hit the edge of a normal tile, it is possible to jump off it without changing gravity. This is easiest with the Child, but any character can pull it off. Another is that if you are lucky, it is possible to run on top of the whole tunnel if you hit the outer side correctly. This is very hard to pull off and will most likely lead to a death if attempted.