I think like many other terms like 'cloud', 'private', 'start up' there is a lot of gray area :). It's up to you where you draw the line. For me, self-hosting means running software in a manner where I have control of the data/application code and the server. With that definition, running software on EC2/DO/Linode is self-hosting. When I self-host using these servers, I know what the server is running and where the data resides.
Also, I think there are other similar popular terms. For those who run in their own premises, the term is on-premise. For those running it home, usually they call it home lab/NAS/home server. Self-hosting to me encompasses all this.
Also, self-hosting doesn't necessarily mean just open source. There are some amazing closed apps out there that you can self-host - emby, confluence, teamspeak to name a few.
I think it's also important to highlight that perfect is the enemy of good. I moved from Google services (A) to an open source platform... that I was paying them to host on Google Cloud (B). Sure, it's still at Google, but the ability for Google to mine data from it is significantly reduced. Of course, later, I moved to hosting it in-house (C), where I have direct physical control.
It's likely if my choices were A or C, I'd have never left A. But that B option eased the transition for me, and made it possible for me to get to the point I felt like the investment was worth it to create a fully on-premise solution.
There's a part D to this too, actually: I'm still using a service to manage the DNS and TLS for it. Eventually I should be able to move away from that too. But without the intermediate step, it'd be too prohibitive and frustrating to have moved to step C.
Great point about D. I self-host at home (it's a thinkcenter m600) but it depends on external services. I use DO DNS and Let's Encrypt TLS, backup to S3. Not to mention I rely on comcast for internet and public IP!
Also, I think there are other similar popular terms. For those who run in their own premises, the term is on-premise. For those running it home, usually they call it home lab/NAS/home server. Self-hosting to me encompasses all this.
Also, self-hosting doesn't necessarily mean just open source. There are some amazing closed apps out there that you can self-host - emby, confluence, teamspeak to name a few.
Two of my favorite spots - https://github.com/awesome-selfhosted/awesome-selfhosted and https://www.reddit.com/r/selfhosted/