A conspiracy, also known as a plot, ploy, or scheme, is a secret plan or agreement between people for an unlawful or harmful purpose, especially with a political motivation, while keeping their agreement secret from the public or from other people affected by it.

Conspiracy come from the Latin word conspiro, as con- means "with" or "together", and spiro means "I breathe", literally meaning "I breathe together with others".

Let that sink in :)