Z Seam or Vertical Seam

Our 3D Printers go one layer at a time. There is a beginning and an end to all things and the same is true for 3D Printing. Likewise, a Z Seam is an inevitable part of 3D Printing.

Your slicer's job is to take a 3D model and slice it up into thin sections, we call these layers. The layers are further broken apart into perimeters and infill. You specify how many perimeters you want it to make and the percentage of infill you want (so you don't waste plastic filling in the inside of a model).

Since the software engineers and mathematicians developing Slicers have not figured out the proper algorithms for something akin to an Infinite Loop we are left to deal with Z Seams.
Depending on your slicer - take Cura for example, you are able to specify the best possible outcome for your particular 3D Model. Once you've got your 3D model situated in Cura, in the search bar type in "Z Seam" and you will see the different options available to control its placement.
User Specified - lets you select which side of your print the seam is placed on.
Shortest - usually puts the seam in the same spot because it's ending the perimeter where it began.
Random - can be good, as it sounds it starts each layer in a random spot, therefore, ending in a random spot too.
Sharpest Corner - this one seems to work very well for angular 3D models.