Window Glazing Trim

[John Stephenson]

.....

[Jim Luttrall]

The glass to frame seal on most metal windows is the flat surface of the inside of the glass which is adhered to the flat surface of the frame.
That in the picture just looks like a buildup of crap over the years, maybe started out as overage of sealant. The plastic trim does nothing to seal against water, it is just a trim for glass retention and appearance.

[Richard Rushing]

I believe that is called a glazing bead.

RR

[Eric Barker]

Glazing bead - bingo!

Buildup of crap - what's not to understand?