ever seen sixth sense?

just kiddding.
it's an umemphasized note.
not really sure how to explain, it's sortve a note played softer (i think)
light as you can pick, sometimes I play single ghost notes as the lowest volume hammer-on that I can get, provided that a pick attack isn't needed. Basically, if you're playing slowly enough, take the pick, turn it completely sideways, and 'brush' the string. Then learn to do it with your pick the way you regularly hold it. Don't give it a full pick attack, just light as a feather.
its a note picked very softly, technically the notes before 'piano(p)' ,for example pianissimo(pp), can be considered as a ghost note .
A note that is picked really quietly and almost cannot be heard - therefore the name, ghost note.

Squier Tele Custom ii (p90 version)

Orange Crush 10

Fender CD140S