What constitutes a merge conflict in Git?

Question

How does git determine that a particular merge has a conflict and what the conflict is?

My guess would go something like this: if the two commits being merged have a

Answer 1

I don't think the merge algorithm has anything special with Git: it is a classic 3-way merge algorithm (not the Codeville one), which can be used with several strategies (default: recurse, or resolve or octopus). The result is a fairly simply merge process which is described here.
Any visualization need is then delegated to third-party merge/diff tools.