A quote from Reuters:
"The agreement was ratified by parliament," Borislav Stefanovic, a senior party official, told the Beta news agency.
Why is there no definite article before parliament? Is that OK?
IMO, the word 'parliament' requires the definite article the. That's because Borislav Stefanovic is talking about a particular parliament that ratified the agreement.
As I said in my comments, why the article isn't there could be due to two reasons. It is, after all, a quote i.e. someone said it in a colloquial style. And secondly, it's spoken by a non-native speaker.
So, grammatically yes, it does require the definite article.
Google's n-gram viewer shows that both uses are possible. However, I would spell them differently:
In 1, "Parliament" is used as a proper noun and hence it doesn't admit the definite article "the". In 2, "parliament" is used as a common noun and hence the definite article "the" is necessary to indicate that the speaker expects us to know what parliament they are referring to.