Geographically, it reaches all continents, including Antarctica (Russian scientists on Bellingshausen Station[1]), but mostly it is based in Russia.
The term Runet is a portmanteau of ru (code for both the Russian language and Russia's top-level domain) and net/network.
For ordinary users, the term Runet means that the content of websites is available for Russian users without foreign language skills, or that online shops have an office in Russia (for example, Russian search engines, e-mail services, anti-viruses, dictionaries, Russian-language websites occupying niches similar to those of Facebook, Amazon, YouTube, eBay, PayPal, Foursquare, etc.
This is also more or less applicable to most post-Soviet states, who use the Runet and are forming a common lingua franca community like English on the Internet.
Russian is the most used language of websites of several countries that were part of the former Soviet Union: 79.0% in Ukraine, 86.9% in Belarus, 84.0% in Kazakhstan, 79.6% in Uzbekistan, 75.9% in Kyrgyzstan, and 81.8% in Tajikistan.