An "establishment" is the official umbrella term for commercial businesses that offer sexual services—regardless of whether they call themselves a "salon," "brothel," "massage parlor," or "bar." What matters is the actual activity, not the name on the sign.
Establishments are subject to cantonal licensing laws. In Zurich, Basel, Bern, and other cantons, an explicit license is required. The authorities conduct regular inspections to verify: fire safety, minimum age, the immigration status of sex workers, and whether the activity is voluntary.