Read the forum, all of your answers are there!!
What is a clearance?
A clearance is the removal, by electrolysis, of all hair present in the area, where some add the caveat of all hair that is visible to someone standing a certain distance away.
Why must one go in for several “clearances?” Once a hair is removed, is it not gone forever? Or is it possible that it comes back?
Once it is removed it is gone. However each of your hairs go through cycles of being dormant and growing. At any one time, not all of your hairs are growing, so while you remove all of the active hairs, there will be more hairs becoming active. Depending on your strategy, you may go and have periodic “clearances” or you may prefer to work for shorter amounts of time over the same period.
Also, why must one “not touch” a hair for a certain period of time and how long should the “no touch” period be?
You can remove hair at the surface, e.g. cutting or shaving. you can make it less obvious by bleaching.
If you tweeze or wax the hair, that will affect the root. you may remove it totally so it will not appear again until it is next in its active phase. This means that the process will take longer.