Mashing is soaking grain in water at a certain temperature (or several temperatures) over a period of time to create sugar for yeast to ferment. Sparging (this is the step not all brewers do) is a process that some all grain brewers use to rinse as many remaining sugars as possible out of their mash.
Mashout. Mashout is the term for raising the temperature of the mash to 77 °C (170 °F). This stops the enzymatic conversion of starches to fermentable sugars, and makes the mash and wort more fluid.