Cycling Socks, much like everyday socks, come in many different styles and types. They may be a regular ankle-cut sock, or a "euro-style high-cut" sock. There are also thicker winter socks (often with a wool mix), and thinner summer socks made of lighter wicking fabrics.
Cycling Socks are made for the specific purpose. They tend to have stronger elastic on the cuffs to hold them up even with leg movement. They also tend to be made of fabrics that will keep your feet at a comfortable temperature, rather than overheating or freezing.
For summer cycling look for socks that use CoolMax fabrics or similar wicking materials, these help disperse moisture build up. For winter socks consider those that have wool mixes, as these stay warm even when wet. Of course, colour and personal preference is also a big part of sock choice.
Your feet work really hard on a bike and are a major point of contact, so it's worth pampering them a bit. Cycling socks are designed to relieve the pressure points generated by pedalling and keep your skin dry by wicking moisture away. Blood flow is also important through your feet, so a cool, vented foot will allow this better than a hot clammy foot.