Wikipedia tells us: "A data library is a collection of numeric and/or geospatial data sets for secondary use in research." This is a good start but is for me a little narrow: I see no reason why textual fields (for example) could not be contained in a data library's data sources. Further, "secondary use in research" is arguably also a little narrow (depending on how you define "research").

I also use this definition, and I agree with You that this definition was little narrow. I need more explanation about data library and everything related, but it's information source also limited.