Hans Hagen
Omega was to a large extend about supporting scripts and fonts for them and when doing so you sometimes need to indicate the boundry of words or glyph runs (regular tex also has a boundary char in the fonts).
first hit on "omega leftghost"
http://torus.math.uiuc.edu/jms/tex2mathml/omega-1.23.4/src/web_omega/omfont....
Using Startpage.com (anonymized Google) on my workstation, "omega leftghost" does not give the hit (under the first ten results). The same for Google.com on my workstation, both when I am logged in with my Google account, and when I am not. On my phone, I get the hit as the 8th result of a Google.com search without being logged in. Maybe (the way you use) your search engine has permitted it to get to know your biases and serve you better. Maybe something else is different. Nonetheless, I did not search for "omega leftghost" yesterday. At this stage of getting into (ConTeXt) LMTX I just want to get a (necessarily somewhat superficial) high-level overview of the entire low level, so to speak. Strategically, I postpone reading source code until after having this overview, because I imagine that I will be much better equipped for that with a rough mental map of the territory, a rough understanding of the purpose of each element I may encounter. Hence, I only searched for expository material, and used only "ghost" in searches and not "leftghost" or "rightghost", because I assume that matching expository material would use the term "ghost".
(thinking of it, i'm not sure if we should keep it because I'm not aware of fonts that have kerns wrt left and right ghist glyphs; we do have a boundary node system instead)
I am definitely sure now that I can forget about ghost nodes for the foreseeable future. Thanks for the answer!