All the pictures are taken from pixabay.com and edited by me!
All are free for commercial use and no attribution required!
As you see in the picture. We have exactly 4 pcs related. No intermediate. People owning those computers are connected with each other and noone else can connect to that network to change something or to know what each user is doing. They can set their rules of communication and respect them. They can work on a same project. So, they are free to do what ever they want. And they still in a decentralized network.
But in case an other one connect to them and start to dictate rules to them, it will not be decentralized anymore. Because the fifth one decided to play the role of the police and to control everything done by those people. In this case those four people aren't free to do what ever they want. So, they are limited by the fifth player and their connection is centralized in this case !
But in case those people will decide to share everything happening between them to the public, they are also allowed to do so. In the case they still decentralized without the fifth guy. In case this person connects to them in this case, it depends only on him/her if the network stays decentralized. So, there will be two choice, or to keep the control up and the dictatorship will be public, or private. Some may call the public control and dictatorship decentralization, so only the private will be considered centralized. But in fact the decentralization is not about being public or not, but it's about the lack of dictatorship and control.
The idea of decentralization started by the consept of p2p. That means from people two people. Non of the authorities will be able to touch the connection in any form. It doesn't matter if that's related to governance or economics. The governance is related to authorities and economics related to banks who may take fees for any transactions while those four people can send money to each other without paying the intermediate for just connecting to them.
So, the decentralization is the relationship between people that should be free from any rulers dictating rules or beneficiaries taking money from non existent service.