I have printed 1 model 3 times with different settings (different temperatures and different bed temperatures).
All 3 models show 1 "line" at some point. The models are smooth all around, but then there is this 1 line on each model.
What is this error called, please?
This is the Z-seam, or just "seam". It's a consequence of the fact that the extrusion of each layer has to start and stop at some point rather than being a continuous path for the whole print (like it would be in "vase mode").
Depending on your retraction speed and distance, travel speed, linear advance/pressure advance tuning, and various slicer-level knobs, the seam can range from mild and nearly imperceptible to a giant bulge to a gaping hole in your print. Yours doesn't look terribly bad.
Most slicers (you didn't mention which you're using; knowing that could help get better answers) have options to control where they position the seam, letting you hide it in corners where possible or put it consistently along one edge of the model you don't care about.
I had the same concern to make mechanical connections where we tolerate a distance of 0.1 mm and these so-called "sewing points" making it impossible. I started to compare between the preview before printing in the slicer and the part printed before.
The problem is recurrent along a vertical line and always repeats itself at the same point. So by looking to the layer settings, there is a junction between the outer and the first inter shell. This junction could be avoided by modifying the "shell print order" parameter.
Here is a video shows the difference abd before / after picture. The line remains visible but the points disappear completely. You can set the layer height to 1.2 mm for better results.
