on Writers in the Storm:

Looking for a quick effective way to take your writing up a notch? Subtext. K.M. Weiland calls it the black belt of fiction writing. When you can replace spoken dialogue with silent communication, with familiarity, shared goals, etc. you invite your readers deeper into the story world.
We employ silent communication all the time in real life. If you’ve been in a long-term relationship of any kind – think back to your parents, siblings, highschool, college, your marriage – all of these relationships (both professional and personal) will utilize silent communication – subtext.