Consider, for example, light bulbs. You can go to any store and buy any brand of light bulb and be sure it will fit in your lamp because the threads at the base are standardized. This allows many companies to make bulbs in competition with each other. They can make large numbers of bulbs because anyone can use them. They can innovate by coming up with more energy efficient bulbs, colored light, etc., and can rest assured their bulbs will work with any lamp.
We also have standards for connecting computers to LANs.
Probably the most standard medium is Category 5 (Cat 5) cables like those connecting the computers on our campus. Cat 5 cables have several copper wires inside the insulation and standardized connectors on the ends. "Cat 5" means they conform to a standard design ratified by the American national Standards Institute. If a cable conforms to the Cat 5 standard, you know it can be plugged into a computer and connected to an LAN. Here is a picture of a Cat 5 cable:
WiFi radio links are another popular LAN connectivity standard. WiFi radios conform to a set of standards, called IEEE 802.11. The 802.11 standards were defined and agreed upon by a professional society called the Institute for Electrical and Electronic Engineers (IEEE). There are actually several standards in the 802.11 family, and new ones are under development. Each has a letter in its name, for example 802.11a, 802.11b, 802.11g, etc. You will see them referred to as, for example, IEEE 802.11a.
There is also an equipment manufacturer's trade association for many technologies. These trade associations are responsible for promoting and marketing the technology and for testing and certifying equipment to be sure that it complies with the standard, that it interoperates with other manufacturer's equipment.
See this paper for a presentation of the history of wireless local area networks -- the "battle" between competing standards and companies and the impact of FCC regulations in determining the outcome.