This post describes and uses some plumbing terms and definitions of the different kinds of home plumbing pipes and devices. This is intended to help you understand more about your home plumbing and possibly describe your situation to a professional plumber or plumbing contractor.
Copper pipes and fittings
Function: Most commonly for water supply, also used for gas supply and on rare occasions 1-1/2 inch or larger is used for waste piping.
Description: Water supply and Waste: Fittings and pipes will be joined by soldering. There will be a minimal change in diameter (about 1/16 inch for 1/2 or 3/4 inch pipe/fittings) when transitioning from a pipe to a fitting.
Galvanized pipes & fittings
Function: most commonly for water supply piping and drain pipes up to 2 inch
Description: Can see threads (grooves) where the pipe meets a 90 (elbow) or tee fitting. It will be the same size (1/2 inch to 1 inch) and many times look the same as the gas piping. Drain pipes will be 1-1/2 inch to 2 inch. There will be a very noticeable change in diameter when there is a transition from a pipe to a fitting.

Hosebib

Homeowners refer to this as a garden hose faucet. There should always be a shutoff in the house to isolate this valve during cold weather. Typically there will be a small cap on the side of the valve to allow water to be drained out prior to freezing weather.

Sewer Pipes
Function: They are a special type of waste pipe. They are underground and carry waste water from a building to the sanitary sewer under the street.
Size: Almost always a minimum of 4 inches in diameter.
Material: No need to know.
Stop & Drain valve
Function: Most commonly used for shutting off the water inside of the home supplying the hose-bib (garden hose faucet). This allows the pipe through the outside wall to be drained before freezing weather so it does not rupture and flood the basement.

Supply Pipes

Function: They carry hot or cold water to your plumbing fixtures. They not only have water in them at all times AND under pressure.Size: ½ to 1 inch in diameter (about the size of you thumb or small finger)Material: Can be helpful to know when communicating with the plumber
Galvanized: Silver/grey. Should see threads at the end of the pipe where it joins a fitting (elbow or tee). Significant diameter change where pipe joins a fitting.
Copper: Orange. Very slight diameter change at a fitting.

Waste Pipes
Function: They carry used water from any plumbing fixture in a building to the sanitary sewer. They only have water in them when a fixture is in use (or if there is a clog in the pipe).
Size: About 1-1/2 to 4 inches in diameter (about the size of your wrist to the size of your thigh)
Material: Not very important to know or communicate to the plumber. Usually black if they are Cast iron (somewhat rough surface and large hubs/fat sections where pipes come together) or ABS (smooth, plastic). The smallest size (1 ½) may be silver (Galvanized). On rare occasion, orange (copper).