student

[joseph boulos]

the dinner is ready.
is this right?? or dinner is ready.

[boothling]

Where I come from (England), "dinner is ready".

[MikeNewYork]

the dinner is ready.
is this right?? or dinner is ready.

As an announcement, it would be more common without the article, but the other is not wrong.

[Humble]

Hi, Josef,
No articles are usually placed with meals:
Is lunch ready?
Supper was later than usual.
Tomorrow you'll have to cook breakfast yourself.

When we tell sth particular about a meal, however, we do use articles.
It was a superb dinner.
There's a modifier-superb
The lunch we had at the Smiths' didn't appease my hunger.
There's a restrictive clause -(that) we had at the Smiths'.
Hopethis helps.