What are those meaningful words which can be read both the way?

You're looking for palindromes! These are words or phrases that read the same backward as forward. Here are a few examples:

Short words:

* madam

* level

* rotor

* racecar

* noon

* pop

* wow

Longer words:

* deified

* repaper

* stats

* kayak

Phrases:

* A man, a plan, a canal: Panama!

* Was it a car or a cat I saw?

* No lemon, no melon!

Let me know if you'd like to see more examples!