Stranded Wire vs Solid Wire
Wire can come in one of two forms, stranded or solid core.
Solid wire, also called solid-core or single-strand wire, is composed of a single piece of metal wire. One very common type of solid wire is known as wire wrap. Solid wire is useful for wiring breadboards, and is cheaper to manufacture than stranded wire and is used where there is little need for flexibility in the wire.
Stranded wire consists of a number of small wires bundled or wrapped together to form a larger conductor. It tends to be a better conductor than solid wire because the individual wires collectively comprise a greater surface area, and is much more flexible than solid wire of equal size. For this reason, stranded wire is used when the wire needs to move around frequently, in a robot arm for example. Conversely, solid wire is used when little or no movement is needed, such as prototyping circuits on a breadboard. Using solid core wire makes it easy to push the wire into a breadboard, while trying to use stranded wire on a breadboard can be very difficult.