Question

What does it mean when astronomers describe the Milky Way as being 100,000 light years wide?

Answer 1

Like a star having its own gravitational system, MW is a system governing its own star systems. Within the limits of advances in detection of far distant stars in MW, its width is estimated.

Explanation:

Currently, the estimate is 130, 000 light years.
This is only 2-sd precision in measurements.
Compare the semi-major axis 9-sd measurement 149598262 km, in a very small astronomical distance unit km
The sd-precision is limited, for far distant stars and galaxies.