The count
Premarket volume is the number of shares that changed hands before 9:30 ET. It is a count of prints, not a verdict.
A large number on a small name can still be a handful of prints. Look at the size of each print, not only the total.
Compare it carefully
A fair comparison is a recent regular session, and only when both counts are on the page you are reading. One count alone is not "heavy" or "light."
The bid and the offer still matter. A lot of shares can print while the spread stays wide.
What not to invent
If the data page does not show the count, the count is not stated. Do not borrow yesterday's number. The cash open is a separate session, with its own prints.
General market news. Not investment advice. The author may hold the Runner Flag name and does not trade it before the 9:30 ET open on the publication day.