Fish tape is a tool which is used to pull wiring through walls, conduit, and similar environments. Despite the name, this tool has absolutely nothing to do with fish. Hardware and electrical stores often sell fish tape, with a range of lengths and styles available. Most is made from stainless steel, which is used to form a flat tape, but other materials can be used as well.
Manufacturers produce fish tape on a reel. Reels are useful for storage, ensuring that the tape is easy to contain and that it will not be damaged when not in use. The reel also gives the fish tape a slight curve, which can be useful when it is being manipulated through a wall or section of conduit. To use fish tape, the reel is carefully unspooled and used to feed the tape through the desired area until it comes out on the other side. This can take some practice and skill, especially if the tape is being fed through a lengthy opening.
Once the fish tape comes out, wires can be attached to a hook on the tape, and the tape can be gently pulled back, bringing the wires through. This usually takes two people, one to handle the wires, ensuring that they don't become snagged or tangled, and one to manipulate the reel, bringing the wires through slowly and steadily. For especially thick or large wires, some people prefer to attach a rope to the fish tape, bring the rope through, and then attach the wires to the rope and pull them through with the rope instead of the tape.
The "fish" in "fish tape" comes from the idea that one is essentially fishing for wires. Learning to work with this tool can be a bit challenging at first, as can working with unfamiliar fish tape which someone does not have a feel for. It can help to practice independently with long tubes or other practice materials to gain experience before using this tool on a job site.
For situations in which wires need to be brought through an especially long opening, two pieces of fish tape can be linked together to do the job. Electricians can also choose between reels with different lengths of tape for various jobs. Reels are usually marked with their lengths, and they may be color coded to make it easy to grab the right reel in a hurry.