Fallen Angels and Demons Are Not the Same.
Fallen Angels are the original Watchers who sinned in Genesis 6 by taking human women and creating genetic abominations. They still possess heavenly (though corrupted) bodies and powers. The 200 Genesis 6 Watchers are all now chained in Tartarus, as stated in 2 Peter 2:4 and Jude 1:6. However, other fallen angels are still active in high places, ruling over nations and spiritual territories as seen in Daniel 10:13 and Ephesians 6:12.
Demons, also called unclean spirits, are the disembodied spirits of the Nephilim, the offspring of fallen angels and human women destroyed in the flood. They are earthbound, restless, and hostile. They crave to inhabit human bodies, as stated in Luke 11:24. Jesus cast them out often during His ministry, including the case of the man possessed by "Legion" in Mark 5:9. They fear being sent to the Abyss, as shown in Luke 8:31. They are not angels and do not have angelic power or form.
The key difference is that fallen angels are the fathers, while demons are the cursed spirits of their unnatural offspring.
This distinction is made explicitly in the Book of Enoch and is fully consistent with Scripture.