Nipple
Nipple turns up in 2 fields: valves, electricians. Here is what it means to the people in each one.
Nipple in valves
A short length of pipe, threaded or plain on its ends, used to connect two fittings or a valve to a fitting.
Nipples are described by size, schedule, length and ends: TBE for threaded both ends, TOE for threaded one end, and PBE for plain both ends ready for socket welding. Common lengths range from close (all thread) through shoulder and short to several inches. Small bore nipples sticking off a vibrating line are a well-known fatigue failure point and are often braced or upgraded to heavier schedule.
"Need a 3/4 by 4 inch schedule 80 nipple TBE for the drain, and a cap for the end of it."
Nipple in electricians
Short length of conduit, threaded or with fittings on both ends, connecting two nearby boxes or enclosures.
A nipple is any piece of conduit 24 inches long or less, often a factory-threaded length of rigid or a short cut of EMT with connectors, joining a panel to a gutter, a disconnect to a transformer or one box to another. Code treats nipples specially: they may be filled to 60 percent of their area instead of 40, and conductors in them need no derating for the number of current-carrying wires. Factory rigid nipples come in set lengths, from close nipples threaded end to end up to 12 inches and beyond.
"Use a two-inch nipple from the panel into the gutter, at that length you can fill it to 60 percent."