Is there such a thing as an Ethernet cable or technically no? Are they actually called UTP cables?
UTP cables are found in many Ethernet networks and telephone systems.
The accurate answer is that they are not Ethernet cables. The cables themselves are not limited to transmitting Ethernet, nor is Ethernet restricted to using just UTP cables.
In the first case, they are often used with many different types of signaling, including as examples voice and serial.
In the second case, you can run Ethernet over coax, fiber, or shielded cables as well.
However, it is common for people to call them Ethernet cables as this is probably their most widely used purpose. So from a "connotation" standpoint, it isn't entirely inaccurate to call them Ethernet cables, especially when dealing with non-technical users.
Some distinctions and history: Ethernet and other networking systems can use a variety of physical media, including fiber optic and metallic wires. Since the wires are almost always made of copper, people usually speak of fiber vs. copper. The original 3 MBps Ethernet developed by Xerox in the 1970s used 50-Ohm RG-8/U coax cable. Later a version using the thinner RG-58 50-Ohm coax was introduced. Eventually several different standards emerged which used twisted-pair cabling.
The "twisted pair" means that, no matter how many conductors there are in the cable, they are arranged in pairs (for example orange and white-with-orange-stripe, green and white-with-green-stripe, etc.). The twist is important for properly carrying electrical signals down the wires, for several reasons. 1) Each signal is sent down a separate twisted pair, rather than using several signal wires plus a single shared ground. This produces less signal distortion, especially at higher frequencies. 2) The twist reduces "cross-talk" and other forms of interference between the signals in the same cable, and between cables. The wires act like antennas, so they send and receive electro-magnetic waves; if two wires are next to each other, a signal on one will be picked up by the other. The twist reduces this.
Twisted-pair cables can be either STP (shielded twisted pair) and UTP (unshielded twisted pair). As the name implies, STP adds a conductive layer (typically metal foil) surrounding either each pair or the entire cable. This shielding helps reduce interference from electrical sources outside the cable. If the individual paris are shielded, this also reduces crosstalk.
Look at the cable connecting your telephone to the wall. Assuming this is a conventional analog system like you would find at home (not a digital PBX or VoIP), all the conductors are parallel, rather than arranged in twisted pairs. For carrying a single voice signal, this is fine. But if you have many signals in the same cable (as in the thick cables that serve an entire office), you would hear other people's conversations if these cables did not use twisted pairs. So, those thick cables always use twisted pairs.
Look again at that phone cord. If you hold the two male connectors next to each other, facing the same way, you will see that the colors of the wires are in a different order. In fact, according to the spec for phone cords, they are always supposed to be "crossover" cables. That is, whatever color wire is all the way to the left at one end of the cable, must be all the way to the right at the other end, and so on.
OK, what about TP Ethernet cables? First off, the standard cables are all "straight-through." That is, the wire connected to the pin all the way on the left in the connector at one end has to be also be all the way to the left on the other end.
But you cannot just connect all the wires straight-through; you have to pair them properly on the eight pins. The TP Ethernet standard says that the two pins closest to the center of the connector must be attached to the same twisted pair of wires. The next two farther out must connect to another pair. The others are different; the two all the way to the left are a pair, and the two all the way to the right are a pair. And the computers, switches, and other equipment have their female jacks wired to take this into the account.
Note: they do make crossover Ethernet cables, which are used to connect, for example, two Ethernet switches together. If you look at one of these, you will see that the wire colors at the two ends are neither the same nor mirror-images of each other. Instead, they cross over so that the signals traveling along the cable in each of the two directions arrive at the right pins. However, many modern switches can sense what is at the other end, and the type of cable, and compensate for it.
One more thing: One of the differences between, say, a Cat 5 cable and a Cat 6 cable is that the Cat 6 twists more often and requires that the twist be maintained closer to the connector. This is one of the reasons it can handle the higher data rate.
What is the result of all this? If you tried to use an Ethernet cable to carry a telephone signal, it might work. But if you tried to use a telephone cable to carry an Ethernet signal, it wouldn't work.
So what about STP vs. UTP? While both can be used for Ethernet, UTP is much more commonly used, especially for new installations. The lack of shielding makes UTP less expensive and more flexible than STP, and the superior interference rejection of STP is usually not needed for acceptable performance. If you go to a computer store, you are much more likely to see UTP than STP, both in bulk cable (such as that intended to be installed inside a wall) and in patch cables which are sold with the connectors already attached.
UTP is a general-purpose/universal cable that can be used for, among other things, T1 lines, Ethernet, and serial communications (read: Junos serial console cabling).
Ethernet merely uses most/all of those pairs in the 4-pair (regular/poe), other technologies may not use all of the unshielded, twisted, pairs available in your standard UTP cable offering, like your standard telephone.
Ethernet cabling, lastly, may now be classified as "UTP for Ethernet" as the standards for 10Gbps Ethernet and higher have more demands for quality versus distance than previous Ethernet speeds (read: 10Mbps).