What exactly does the label "Hermetic" refer to?

This question has been on my mind for a while. I get that it's a form of water/dust protection - but what is it in fact? Is it a seal, a case shape feature, a way to secure the back? Does anyone perhaps have a photo do demonstrate?

How does Hermetic differ from solutions in other contemporary Swiss watches?

Honestly I feel that most watch companies at the time just tried to come up with a name that would be unique and recognizable, imply a specific ability to the watch (whether true or not), and stick in the mind of the consumer.  "Hermetic" obviously meant to convey that the watch is hermetically sealed (sealed in a way that is completely airtight and prevents the passage of any gases, liquids, or solids, ensuring a tight, impermeable barrier), but the Hermetic cases were no different than those of other brands at the time.  They had a moisture/dust barrier consisting of an acrylic crystal frictioned in under tension, a gasketed crown, and caseback gasket.  If the name convinced potential buyers that the "Hermetic" was more moisture resistant than the "Seamaster", "Waterking", or the "Sea Lord", and resulted in more sales then mission accomplished.

Thanks for replying.

I get the marketing angle, thats clear with most brands. Zoduron (the unbreakable mainspring) is probably another example.

Yet one thing caught my attention and made me wonder: On the catalogue site, a 1960ies guide on how to sell a Zodiac is available. On page 22 a special water-proof case construction is mentioned, that was (it is claimed) particular to Zodiacs watches. Could this be what Hermetic refers to?

I still feel that it is more marketing aligned, but someone else may have more insight to that than I do.  If there is something unique and specific to the Hermetic cases in particular, I may not have seen it yet.  I have worked on a "few" Hermetics over the years and have only observed them having the standard technology of the time for moisture resistancy.