Source Rock
The organic-rich rock that generated oil and gas over geologic time; in a shale play it is also the reservoir, produced directly via fracturing.
Source rock is the organic-rich rock — usually a dark, fine-grained shale or mudstone — that actually generated oil and gas. Buried deep enough, the heat and pressure over millions of years "cooked" its trapped organic matter into hydrocarbons, which then either stayed put or migrated upward into porous reservoirs.
In conventional plays the source rock and the reservoir are different rocks: oil is born in the source rock and migrates into a separate, more permeable layer that a well taps. In a shale play, the source rock never gave up its oil — so operators produce it directly from the source itself, which is why those wells require horizontal drilling and fracturing.
For owners, the takeaway is simple: a thick, oil-rich source rock under your tract is the geologic reason a modern shale well can be drilled there at all, and the reason your minerals may be worth leasing.