A fairly vague geographic term that refers to the middle (in terms of latitude) of the Asian continent.
The term usually includes Kazakhstan, Uzbekistan, Tajikistan, Kyrgyzstan,Turkmenistan and Mongolia. More broadly, the term can include Afghanistan, northwestern China, parts of southern Russia and, less, commonly, Iran.
Guy 1: "I went on holiday to Central Asia last February."
Guy 2: "Central Asia? What's that, like Nepal?"
Guy 1: "No man, Nepal's not in Central Asia, I went to Kazakhstan, Uzbekistan and Kyrgyzstan."
Guy 2: "What the fuck? There's a country called Kyrgyzstan?!"
Guy 1: "Yeah man, it's a great little country!"