A peak lapel points upward. Instead of a notch cut into it, the outer edge rises past the collar in a point. It came from double-breasted suits and evening dress, so putting one on a single-breasted business suit is a deliberate move and it looks like one. Nobody chooses a peak lapel by accident. If you buy suits to clear the minimum bar of looking professional, the notch will serve you perfectly well. If you have actually thought about what you wear and enjoy thinking about it, this is the one you have been circling.
Peak or notch, and when each one is right
The notch is the default on single-breasted suits and it deserves to be. It is correct in every business and formal setting, it proportions easily across very different builds, and everybody understands it on sight. There is nothing second-rate about a notch lapel. It is the safe answer and the safe answer is usually the right one.
A peak on a single-breasted suit does not make the suit more formal. It makes it more personal. It is bolder, it has more structure to it, and it is a good deal harder to get right than a notch. Cut well it looks superb. Cut badly, wrong width, wrong angle, or set on a body it does not suit, it looks slightly off and everybody senses it even if nobody can name the problem. That is the whole argument for having it cut by tailors who have made hundreds of them and know the geometry by feel.
Scaled right, a peak lapel works on most men. It is particularly good if you have broad shoulders, because the rising angle plays to the width of the chest. Shorter men tend to shy away from it, worried that the upward line will cut their height, but a peak scaled correctly to the frame works perfectly well. Come in and we will pin one up so you can see it on yourself rather than on a photograph.