Septage or "septic tank sludge" is fecal sludge that is accumulated and stored in a septic tank. Septage tends to be more dilute, as septic tanks are typically used with flush toilets (blackwater) and can also include grey water. Septic tanks also tend to have less solid waste, as they only receive things that can be flushed down a toilet (e.g. toilet paper). When operating as designed, a sludge blanket layer accumulates on the bottom of the tank, a scum layer that contains fats, oil and grease accumulates at the top, and the effluent or supernatant contains less solids. 
Septage is periodically removed (with a frequency depending on tank capacity, system efficiency, and usage level, but typically less often than annually) from the septic tanks by specialized vehicles known as vacuum trucks. They pump the septage out of the tank, and transport it to a local fecal sludge treatment plant. It can also be used by farmers for fertilizer, or stored in large septage waste storage facilities for later treatment or use on crops. 
The term "septage" has been used in the United States since at least 1992. It has also been used in projects by the United States Agency for International Development in Asia. Another definition of septage is: "A historical term to define sludge removed from septic tanks."
In India some government policy documents are using the term FSSM for "Fecal sludge and septage management".