Any wire run which uses more than one conductor is called a cable  While some rolls of "speaker wire" etc. may be called wire, they are actually cables. Cabling is used in everything from the smallest project to aircraft carriers and in the Large Hadron Collider.

The diagram below shows a typical cable consisting of three insulated wires:

_{^{"Cable Cross Section" by Marekich - Own work. Licensed under CC BY-SA 3.0 via Wikimedia Commons}}

Selecting The Right Cable

You will want to specify the type of cable based on your application.  Here are some steps to take to specify desired cable types:

1. Count the number of conductors - you will want to know how many power and signal wires you need to go from one point to another.  If you have two wires performing a specific function (like a positive and negative power pair or a signal wire and its ground) then they may be considered a pair.  If they are paired within the jacket by twisting them together this is called a twisted pair.
2. Size the wires appropriately - select the wire gauge for each conductor. For power wiring, size the conductors so the current flowing through them will not heat the wires or provide too much resistance over the given length.
3. Select solid verses stranded wire - most longer cables are stranded wire for flexibility.  Solid conductor is used for smaller wires or specialty wire like that used in residential power in some countries.
4. Shield sensitive signal wiring - cables carrying higher-frequency signals may "bleed" those signals into other conductors or other wires.  Wires that need to be protected from others can be twisted together and/or have a foil-like metal shield around them to provide protection for those wires.  Some wire cabling has a non-insulated drain wire to provide a common ground between two points.
5. Individual conductor covering - you often have a choice of colors for conductors in a cable.  For example a black and red (or white) twisted pair may be used for power and another twisted pair with different colors may be signal wires.  Such a cable would be usually listed as two-pair.  If the wires do not need to be paired together, for example you have four signal wires, you might specify 4 conductors. Four conductor and two pair both have four wires.
6. Overall bundle covering - the jacket is the overall cover for multiple conductors.  It holds all the conductors together, keeps them waterproof and protected.  For signal wiring, the jacket is often grey or black although specialty cabling like for LAN wiring may be of any color.

So as you see, cabling may range from a single pair (two-conductor) to cables with hundreds of conductors like that used in copper phone trunk lines.

^{_{Picture by Robert Scoble licensed under the Creative Commons Attribution 2.0 Generic, Wikimedia Commons.}}

Finding Manufactured Cable

Once you have your cable requirements written down, you can go to a company or shop to find a cable which incorporates the features you need.  

To look up what commercial wire matches your needs, you can go to a specific manufacturer's catalog.  You can do this by one of three ways:

1. Browse the offerings of specific companies like Adafruit. Companies select products that may be useful for specific purposes.  Specialty cable may be offered by companies not offered by other manufacturers or electronics companies.

2. Browse the offerings of a specific cable manufacturer.  Belden has a popular selection of multiconductor cabling as does other companies. For example, specifying Belden 5341, this is 18 AWG with two pairs of wires, non-shielded.

3. You can search a vendor like Digi-key which has a form-based cable finding web page.  The page has menus listing features, allowing one to narrow a search to a specific subset of cabling and the ability to list multiple manufacturers.