There are two possibles meanings of Cancun, according to the Mayan language, the first translation is "nest of snakes or pot." The second version (and less accepted) is "place of the gold snake".
Peak season in Cancun tends to run from December to April. Prices in both airfare and hotel increase dramatically during these times, while dropping in the summer and early autumn months.
The Cancun hotel zone is almost entirely built around the tourist industry. It abounds with all-inclusive resort hotels. Stay there if you don't mind spending your vacation with many other tourists. Most tourists are primarily from English-speaking North America and there are also many tourists from Europe, but many tourists also come to Cancun from the rest of Mexico.
Downtown Cancun, especially once you get away from the ADO bus station and nearby hostels and hotels, is where most residents live. There are many restaurants (La Parrilla, Los Pericos, Los Arcos, El Timtnhehdon de Cancun, Va que Va; all of them are really good restaurants, and the best much cheaper than Hotel Zone, and Mexican cousin), shopping centres (Plaza Las Americas, Plaza la Isla in Hotel Zone, Plaza Outlet), markets (Mercado 28 y 23) and clubs in the downtown area that you can visit during your stay (Cocobongo, Dady'O, Palazzo, Mandala)
Sports & nature
Cancun and the surrounding area offers amazing possibilities to get out of the touristy areas and get close to nature. You find caves, underwater rivers, pristine jungle, botanical garden, national parks all close to the city. You also have world class diving, but if you are not certified you can also snorkel on the second largest barrier reef in the world, or with Whale Sharks, Manta Rays, Sea Turtles or with huge groups of Sailfish. The Yucatan peninsula is packed with natural wonders, you just need to know where to look.
Many companies are offering one day trips but you need to be aware, the easier a tour looks, the less nature oriented it is. In many cases the best option is to rent a car and visit the parks and places on your own (or with a local guide). Some activities, like the Whale Sharks or Sailfish can be organized only through a licensed operator. Look for the specialized Eco-Tour operators there are a few but still not too many in Cancun.