“The other popular step used by modern brewers is the dough-in rest (protein rest). Usually done at a temperature between 100-120 F, the dough in allows the grains to soak and saturate as well as allowing the key various lower temperature enzymes to begin chopping up longer chains of molecules. This will generally lower your pH slightly, and improve your mash efficiency by a few percent. I personally recommend a 20 minute dough in at a temperature between 100-112F for maximum impact.”

http://www.beersmith.com/blog/2009/07/16/mashing-for-all-grain-beer-brewing/

‘Doughing in’ refers to a 20 minute rest @104F where grains are “…mixed with water to allow time for the enzymes to be distributed.”

‘Doughing in’ and ‘mashing in’ are often used interchangeably; however, there is a distinction.

Maybe worth noting that in order to dough in at a given temperature, your strike water must be somewhat hotter than your target temperature, around 12 degrees F, depending on a variety of factors.