"Vaccine efficacy is the percentage reduction of disease in a vaccinated group of people compared to an unvaccinated group"
So basically a 90% reduction in Covid infection.
https://www.cdc.gov/csels/dsepd/ss1978/lesson3/section6.html
So "disease" is probably an infection there, not relatively milder infection.
90% still crushes the transmission rate.
Unfortunately, there's yet another property of vaccine performance: some prevent the virus from reaching any level of footing in the host, others only make the body's eventual response stronger, preventing initial footing to cause heavy illness. SARS2-COV is rather peculiar in how its transmission performance is particularly strong in early, mostly presymptomatic stages, so it's perfectly possible to end up with a vaccine that reliably protects carriers from disease, but does not remove them from the spread equations at all, or only very little.
Pfizer is saying that their vaccine is effective at protecting against CoVID-19 disease. They haven't said anything about preventing SARS-CoV-2 infection yet, as far as I can see. The difference is important, because there are vaccines (such as the Salk polio vaccine) that only protect against disease, but not against infection. People get infected and pass on the virus without ever getting sick, so there's no herd immunity.