The term means an unlawful act committed by two or more people.
9/11 was a conspiracy.
Charles Manson was convicted as part of a conspiracy.
Sacco and Vanzetti were convicted as part of a conspiracy.
They happen all the time.
Almost all drug cases are conspiracies. I mean, who makes a whole bunch of drugs for themselves? No one. They are for sale and distribution.
The term get confusing when we apply it to other situations.
For instance, in the Kennedy assassination... either one.
But more, on that in the future.
For now all I am saying is that this is what a conspiracy is. Nothing more. Nothing less.
The definition for conspiracy can be found here.
My bet goes on definition three.