Wait a minute... Aren't 11x17 & 17x11 the same size?

The answer is Yes and No. Depending on what you will be using the paper for, the "grain direction" of the paper matters.  

Direction of predominant fiber alignment, usually the machine direction. The directionality of paper must be taken into account in measuring such paper strength properties as tear, tensile, and folding endurance. Grain direction can also influence the curl of a cut sheet if it is stretched or moistened.

If you will be folding, scoring/creasing, or binding the paper, it is recommended that you do so in parallel to the grain (aka the "long direction").  

French grain directions are indicated by the order of the sheet size dimensions.
The long grain follows the second number in the dimension.

For example, 25x38 would indicate the grain is long in the 38" direction. If the size is listed as 38x25, the grain will be long in the 25" direction.