Overtourism is the congestion or overcrowding from an excess of tourists, resulting in conflicts with locals. The World Tourism Organization (UNWTO) defines overtourism as "the impact of tourism on a destination, or parts thereof, that excessively influences perceived quality of life of citizens and/or quality of visitor experiences in a negative way". This definition shows how overtourism can be observed both among locals, who view tourism as a disruptive factor that increasingly burdens daily life, as well as visitors, who may regard high numbers of tourists as a nuisance.

Overcrowding or crowding is the condition where more people are located within a given space than is considered tolerable from a safety and health perspective. Safety and health perspectives depend on current environments and on local cultural norms. Overcrowding may arise temporarily or regularly, in the home, in public spaces or on public transport. Overcrowding in the home can cause particular concern, since the home is an individual's place of shelter.