Flashing
Flashing turns up in 2 fields: valves, waterproofing. Here is what it means to the people in each one.
Flashing in valves
Liquid partly turning to vapor through a valve because downstream pressure stays below its vapor pressure.
Unlike cavitation, the bubbles never collapse: the outlet becomes a high-velocity mix of vapor and liquid droplets that erodes trim and the downstream body with smooth, polished, scalloped wear. Flashing cannot be designed out by trim, because it is set by the process pressures, so the answer is hard trim, angle bodies discharging into a larger pipe, and outlets sized for the vapor volume.
"Hot condensate letdown is flashing through the valve, plan on a hardened plug and an angle body this time."
Flashing in waterproofing
Thin sheet metal or membrane installed at joints and interruptions in a wall or roof to direct water back outside.
Flashing goes wherever water would otherwise get into the building: windowsills and heads, wall bases, shelf angles, roof-to-wall intersections, copings and penetrations. Materials include stainless steel, copper, aluminum, lead-coated copper, flexible membranes and composites. Flashing works by gravity and lapping, collecting water and turning it out past the face of the wall.
"No flashing at the window head, water's running down the jamb and straight into the drywall."