A hotspot is a location that offers Internet access over Wi-Fi through the use of a router. Public establishments, such as coffee shops, have 'free-to-access' hotspots for their customers all over the world.
Hotspots can be found using crowdsourced online mapping databases - allowing mobile applications to use this data to provide location-based hotspot finding. Most large establishments provide a free wireless network infrastructure throughout franchises and brands.
Origin - 'hot' as a metaphorical use, 'spot' as a known/identifiable location.