Are Fallen Angels Demons?

It's widely believed that they are the same but are they the same?

“Are Demons Fallen Angels and 2 Other Common Misconceptions” by Michael S. Heiser: https://www.logos.com/grow/bsm-are-demons-fallen-angels-and-2-other-misconceptions/.
“When Did Angels Become Demons?” by Dale Basil Martin: https://www.jstor.org/stable/25765960.
The official Orthoprax Christianity website: http://orthopraxchristianity.org/.