Nothing in particular.

[david11]

Can this phrase be used in response to questions like what's up,what's the matter etc to mean nothing special?

 

[5jj]

Yes, if you wish.

 

[david11]

Yes, if you wish.

Is that usage confined to informal conversation? or can it even be used in formal writing?

For example,

If someone asks what's happening in Parliament? - nothing in particular( to mean everything goes usual)

 

[bhaisahab]

Is that usage confined to informal conversation? or can it even be used in formal writing?

For example,

If someone asks what's happening in Parliament? - nothing in particular( to mean everything goes usual)

It can be used in both conversation and in writing. I wouldn't say that it's particularly formal.