A relative adverb is an adverb which introduces a relative clause. The English relative adverbs are when, where, whenever, wherever and why.

I will never forget the day when I first met you.

Sunday is the day when I am least busy.

Do you know the house where John lives?

That is the place where I was born.

Whenever I go to Paris I try to see Peter.

You can come whenever you like.

I take my cellphone wherever I go.

Whenever I see you I feel nervous.

Wherever you go, you will find Coca-Cola.

Notes

We usually use when and where to introduce relative clauses after nouns referring to time and place. They are used in the same way as preposition + which.

Compare:

I will never forget the day when I first met you. = I will never forget the day on which I first met you.

Sunday is the day on which I am least busy.

This is the place at which I was born.

Why can be used in a similar way after the noun reason.

I don’t know the reason why she hates me. (= I don’t know the reason for which she hates me.)