Nissan NS-2 is a specialized Continuously Variable Transmission (CVT) fluid designed for specific older Nissan, Infiniti, and some other Asian vehicles (roughly 2006-2012), providing smooth operation, wear protection, and optimal performance in JATCO CVTs, but it's crucial to use the correct fluid (NS-2 for older models, NS-3 for newer) as using the wrong type can damage the transmission.