As far I know, unconfirmed transactions are stored in the memory pool. However, in the Bitcoin wiki, I see a data structure called transaction pool. Are they the same thing or not? Also for the orphan transactions, as far as I know they are stored in data structure called orphan pool, right?
That is referring to what is now called the mempool.
The wiki is unmaintained, and contains mostly outdated or incomplete information. I would suggest you use the bitcoin.org documentation instead.