The line where lapel and collar meet is called "the gorge". It is one of the few things in a men's suit, designers and tailors can play with. Depending on fashion, the gorge can fluctuate from very high to very low.
So that's what it's called. Lower gorges make the wearer's shoulders look huge, like an ape's. I don't know, but that's just how it impresses upon me; the lower gorges make it look like the jacket's stooping over. On the other hand, gorges that are too high work to abbreviate the shoulders, compressing them towards a needle point at the neck and head. That's just how it looks to me. Granted, I'm getting higher gorges on my next suit jacket, but it won't be hugely extreme.