1. The mechanism of selection of chains in the blockchain is often called the mechanism of consensus. Such a term is rather misleading than clarifying the essence of the matter (despite the fact that the English word “consensus” was used at the end of his article by the author of Bitcoin, Satoshi Nakamoto).
Indeed, consensus generally refers to the general agreement of participants in some discussion.
However, there is no explicit “discussion” in the blockchain. Moreover, when starting to work with a specific chain, the node does not know whether it is accepted by other nodes, and completely independently accepts or rejects it. In the last case, the rejection of the chain by a specific node does not automatically lead to its rejection by the network as the whole.
It is not too natural to consider the solution of the net as a “common” for it also because some nodes can cease to be active for a considerable time, and then reactivate again, without being able to influence the decisions made in their absence.