I got this question today in my search box:
Can a catholic orthodox priest celebrate mass outside a church?
The person might have been looking for an older article, and perhaps found it.
The ideal is that Mass is celebrated in a consecrated church building. It can also be celebrated in a simply blessed oratory or chapel. It can also be celebrated in a home or a suitable secular building for pastoral reasons (eg: for the sick or a congregation of people unable to afford a dedicated church building).
In a way, where Mass is celebrated, that place becomes a church even if only for a short time. I have celebrated Mass outdoors, for example on a rock on the Glénans islands on on the tailgate of my van using my tuck box chapel. Many priests have done so, because no consecrated church was available to them.