( The first N in this name is pronounced like n in 'no', the Y like Y in 'you' and the last N like N in 'turn'. The last s indicates plural number.)
Naaraayanas were a batch of ten thousand ( or one lakh. The original says ten crore, but all the interpretors took it as ten thousand or one lakh.) fighters whom Krishna offered to Arjuna and Duryodhana when they approached him for help in the war. Duryodhana chose them in stead of non-fighting Krishna.
In the war, these Naaraayanas of the yaadava race, together with the Samshapthakas, attacked Arjuna many a time in the war.