It's annexation when you declare it's part of your permanent holdings. That's totally separate from if you are holding it by force or not.
If an undiscovered, uninhabited island forms in international water, and some country claims it, if they want it in their permanent lands, they will annex it. There's not necessarily conflict or appropriation there.
The issue with annexation of Crimea or the Golan Heights is that the holding of the territory is by force, and annexation is an expression of intent to keep it, rather than simply occupy it on an indefinite but assumed temporary basis.
If an undiscovered, uninhabited island forms in international water, and some country claims it, if they want it in their permanent lands, they will annex it. There's not necessarily conflict or appropriation there.
The issue with annexation of Crimea or the Golan Heights is that the holding of the territory is by force, and annexation is an expression of intent to keep it, rather than simply occupy it on an indefinite but assumed temporary basis.