Shale is a soft, finely stratified sedimentary rock that was formed from consolidated mud or clay and which can be split easily into fragile slabs.
Shales can be rich resources of petroleum (oil) and natural gas. Sedimentary rocks are rocks formed by the accumulation of sediments at the Earth's surface and within bodies of water. Common sedimentary rocks include sandstone, limestone, and shale.
Oil derived from shale contains significant amounts of a hydrocarbon called “kerogen.” When heated and processed, kerogen becomes a light liquid hydrocarbon called “shale oil.” It can be refined into gasoline, diesel, jet fuels, and other valuable petroleum products.
A particular deposit of stratified material that has turned into shale is called a "Play." So you will see names such as "The Marcellus Play " or "The Barnett Play," or the "Haynesville Play," or the "Fayetteville Play," or the "Bakken Play," or "Eagle Ford Play," etc. Go here to find the descriptions of all of the shale plays. You can also find at that website the current price of a barrel of oil.