It means that you're not meant to use their servers to supply your map tiles (basically, image files that cover an area of map). You're supposed to either use o

It means that you're not meant to use their servers to supply your map tiles (basically, image files that cover an area of map). You're supposed to either use one of the commercial tile providers or set up your own tile rendering servers. All the code and data required to produce tiles identical to the ones on openstreetmap.org is open source and freely available so in principle this isn't a big deal. This company just wanted a direct drop-in replacement for Google Maps that didn't require running more of their own servers.