When you hear that lovely song from Karam, you might hear it as Tinka tinka zara zara. Now Tinka means a straw. But then zara zara means 'a little' and doesn't give a lot of meaning to the song. According to me, it's zarra zarra, as Zarra is a common Urdu word meaning a particle, and hence, the line would be 'tinka tinka zarra zarra, hai roshni se jaise bhara, har dil mein armaan hote to hain, bas koi samjhe zara' meaning every straw and every particle, or simply every particle, is like filled with light, every heart has its wishes, just that someone should understand them.'
Here, the last zara is the one that would mean 'just', 'a little.'