The event, which

"The event, which celebrates its 30th anniversary, puts together two bull (male) camels with a female camel on heat nearby."

I found this above sentence and also found

"The event which celebrates its 30th anniversary puts together two bull (male) camels with a female camel on heat nearby." and I cannot feel any meaning difference between them except for "comma" behind the event.

could you tell me what is the difference between them?

The commas are necessary. A version without commas would be appropriate in a context involving several events with distinct anniversaries - not very likely:

Code:

---

The event which celebrates its 30th anniversary puts together two bull (male) camels with a female camel on heat nearby.
On the other hand, the event which celebrates its 20th anniversary puts together only one bull (male) camel with a young
 female camel who is not on heat 100 metres away, and the event which celebrates its 10th anniversary puts together a
small cat and a huge rat...

---

This sort of context is rare (if just conceivable by people with reality problems :-)) so some people might feel that - if the sentence is short enough - the commas don't matter too much. I would disagree.

b

"The event, which celebrates its 30th anniversary, puts together two bull (male) camels with a female camel on heat nearby."
The words between the commas tell us more abouut the event. The commas act like brackets.

"The event which celebrates its 30th anniversary puts together two bull (male) camels with a female camel on heat nearby."
In that sentence, the words I have coloured red define the event. This is likely only if there are other events taking place, and these other events are not celebrating their 30th anniversary.

You two are great!! Sometimes I get confused because some native speakers say different answers to the same question.Thanks for getting me out of the long time trouble.:-)

Thank you :oops: - but I think 5jj's answer was more useful than mine. I thought it wouldn't be too helpful to talk about 'defining' and 'non-defining', but his post actually showed what 'defining' means.

b