Unconventional gas is natural gas obtained from sources of production that are, in a given era and location, considered to be new and different. Sources at times considered to be unconventional include:
As noted by the International Energy Agency (IEA) in 2013, regarding unconventional oil, what is conventional vs. unconventional changes over time as technologies and economies change, Certainly this applies to unconventional gas as well.
Natural gas, whether conventionally produced or not, has itself been considered to be an unconventional source for oil production.
References
Unconventional gas Wikipedia(Text) CC BY-SA