Hi Mayuri,
If you are referring to this article:
For the List Item mentioned in this article means the rows in your list. Columns are not counted.
So you can take 30 million item as 30 million rows.
However, please notice, it's not recommended to store such a large data in a single list.
As it will slow down the performance and the as mentioned in the article as well. It will cause some permission functions like "Stop Inheritance" stop working.
Regards,
Alex Chen