I was trying to calculate pricing for AWS EMR service. I googled out but could not find what is Amazon standard under hadoop distribution column which is default.
Assuming you are talking about the pricing calculator at http://calculator.s3.amazonaws.com/index.html, the "Amazon Standard" choice in the "Hadoop Distribution" dropdown simply refers to AWS EMR's own distribution of Hadoop (and, of course, other BigData apps like Hive, Spark, Pig, etc.). That is, not one of the MapR distributions, which are also supported but have a different cost structure.
This is the default distribution for EMR, so you would know if you were using something else. If you are using a release like emr-4.x, you are using the "Amazon Standard" distribution.