El "muffler" es el silenciador, y el "muffler cutter" es la cola de escape, el elemento final de todo el sistema de cañerías que incluye el silenciador, que comienza en el motor y termina en el "muffler cutter".

Es un trozo de cañería de mayor diámetro que las cañerias previas, en ocasiones con rejillas metálicas para acompañar la función del silenciador, pero primariamente cumple una función estética: que el extremo del sistema que es visible tenga aspecto agradable y no oxidado, a diferencia de los demás elementos del sistema de escape, que está sometido a altas temperaturas.

Referencia de qué es:
"Description:
TECHNICAL FIELD
[0001] The present invention relates to a muffler cutter (i.e., an accessory that is fitted to a muffler).

BACKGROUND ART [0002] A combustion gas (exhaust gas) discharged from an automotive engine is discharged to the outside from the end (tail end) of a tailpipe through an exhaust manifold, a catalytic converter (that is provided directly below the exhaust manifold), a front tube, an underfloor catalytic converter, a center muffler, a main muffler, and the like that are sequentially connected to the engine (see Patent Document 1 (JP-A-2008-190371), for example).
[0003] Most of such an automotive exhaust system (exhaust pipe) (e.g., main muffler) is provided at the bottom of the automobile, and is not normally observed from the user. However, since the end (tail end) of the tailpipe that is situated at the end of the exhaust system (exhaust pipe) is exposed under the rear bumper of the automobile, the tailpipe is easily observed from the user, and significantly affects the appearance of the automobile.
[0004] Therefore, a muffler cutter is normally provided to the end of the tailpipe so that the appearance and the quality of the automobile are improved."
https://www.patentsencyclopedia.com/app/20160053642

Referencia del nombre en español en un sitio de España:

https://www.whatuwant.es/category/tuning y buscar: cola de escape
y surgen muchos productos con este nombre

Referencia en Argentina:

"Nuevo | 82 vendidos
Cola Caño De Escape Deportiva Cromada Universal Para Autos
5 opiniones
MÁS VENDIDO
10º en Colas de Escape"
https://articulo.mercadolibre.com.ar/MLA-908476643-cola-cano...