I read something a while back talking about this. It was a term or phrase I had to lookup; and it was available via Google-Bing, but not “predominant” - not a universal thing.
Not exactly back in the times of the monks: writing flamboyant first characters that take up perhaps 5% of the page (and perhaps 80% of the artistic effort), but I don't think it precludes that.
The context of what I read was more along the lines of turn of the century efforts; perhaps some kind of art nouveau fad. Flowery flourishes. Itself perhaps an echo of 18th century penmanship – calligraphy++.
When a letter to someone was more than just text; and more than the craftsmanship of excellent handwriting.
I think of it like putting a big squiggle under a paragraph (elongated sideways “S”) with two lines through the middle like a dollar sign. That is a minor instantiation of what I'm talking about. The term captures that and much more.
Occasionally you'll see examples online, where the author will have an obscure dingbat glyph at the bottom that kind of captures the thing.