In a modern SLR, there usually is no literal pinhole. The diagram is a simplification of how a lens forms an image.

The closest concept is the lens’s centre of projection, often discussed alongside the entrance pupil or sometimes incorrectly called the nodal point/no-parallax point. It is the point the lens behaves as if light rays pass through when using the pinhole-camera model.

That point is typically somewhere inside the lens, though depending on the optical design it can effectively be elsewhere, even in front of the lens. It is a virtual point, not a tiny physical hole.

The aperture is different: it is the adjustable opening in the lens that controls how much light enters and affects depth of field. A very small aperture can make the system behave more like a pinhole, but it is not the same thing as the simplified 'orifice' shown in basic diagrams.

So: in old camera obscura systems, the hole was real; in modern SLRs, the lens replaces that pinhole and the 'pinhole point' is an optical model rather than a physical part.