What does "a little flesh" mean when using a large aperture?

Meat means not sharp, not clear, or not sharp enough.

Because of the lens grinding technology, the larger the lens, the harder it is to approach the ideal curvature, and the closer the lens is to the edge, the harder it is to approach the ideal curvature. The spherical aberration caused by spherical surface will become obvious with the increase of lens, and the aberration directly affects the clarity of imaging. The smaller the aperture, the fewer lenses are involved in imaging, which can avoid the influence of phase difference caused by technical and theoretical limitations.

The relationship between aperture and imaging can be referred to: /showthread.php? threadid=737473