meaning - What does "seam" mean?

As you know "seam" has several different definitions in English.
But I can't understand its meaning in this context:

How to deal with seams

a. There is no seam. We've finessed the seam so
thoroughly, you can't even tell. This doctor knows everything about
the situation as seen by the last doctor, no need to worry about the
handoff. You can't tell where one part of the railing ends and the
other begins. Your place in the queue and your records and your status
are so clear to the next agent that it won't matter a bit to you that
there was a switch.

b. There is a seam. That was one color, this is a different one. That
was yesterday, this is today. She was your last teacher, I'm your new
teacher.

As you might have guessed, the problematic area is where you try to
hide a seam, and you fail.

Seams are a promise, an opportunity, a fresh start. Own them or make
them invisible.