COVID and masks

The study, reported in the American Journal of Medicine (AJM), is a meta-analysis of articles posted in “the voice of the CDC,” its weekly Morbidity and Mortality Weekly Report (MMWR). The indictment being made is that for the MMWR reports:
I’ve written before on the physiology of wearing masks in order to debunk some misinformation on the impact of masks on childbirth.
To address this fundamental question, I considered state-level data on frequencies of wearing a mask outside the home [1], which increased to a peak in late 2020
"Inserting a filter into a stream of particles will capture some of them." Here are some fundamental considerations.
What do you mean by a mask?