What's the difference between 'collision' and 'conflict'? In SQL language, should I say 'PK collision' or 'PK conflict'?
A collision is usually taken to mean a physical impact: two cars which crash into each other would be a collision.
A conflict is normally between two or more things which disagree in some way, although its meaning can be extended across both tangible and intangible notions. For instance, you can have a conflict of opinions, where someone disagrees with the other, but you can also have a physical conflict (a fight, or a war).
Conflict, used in its physical sense, could be synonymous with collision.
In your case, you should say a Primary Key (PK) Conflict, as — and I'm assuming it's a duplicate here — the primary keys disagree with each other because they are the same.
They don't physically bump into each other.