What mask means in practice
A diving mask creates an air space in front of the eyes and encloses the nose. Fit is individual: the skirt, nose pocket and strap need to work together for the person wearing it. Some models accept corrective lenses.
An example to think through
Two people can have the same face width but prefer different masks. For a useful fitting conversation, describe pressure points and vision needs rather than asking for the most popular model. Bring questions about any corrective lenses you normally use.
A common misunderstanding
Tightening the strap is not a universal solution to a poor fit.
Underlying concept: PADI — Masks. The example is an original YouDive study prompt, not a reported dive.