The reality of so-called "conspiracy theory"

You don't have to be attuned to the news to be aware of this term, often applied to off-mainstream ideas or concepts about what happened--and didn't...-- in matters of the state, politics and it's associations.  

"Oh, another "conspiracy", is the quip or 

"That's just another conspiracy theory" or 

More aimed to discount the source, not just the story, 

"They're just another of those 'conspiracy theorist'."  

Can a conspiracy (theory) actually be the truth on the matter or, as it is considered and conveyed, aimed for the truth?  

For that matter, do conspiracies really happen?  

Do persons of relative power co-conspire, using this compounded power for their collective or common interests?  Do they use DOUBLESPEAK and DOUBLETHINK, going so far as to change or pervert the language, the meaning of terms?  

EVACUATION?

Can they imply something as true or real when in fact it is explicitly false, and can they express or testify falsehoods with impunity; that is, can they get-away-with perjury?   How far and how deep will they go to cover their lies?