A conspiracy, also known as a plot, ploy or scheme, is a secret plan or agreement between people for an unlawful or harmful purpose, such as murder, treason, or corruption, especially with a political motivation, while keeping their agreement secret from the public or from other people affected by it. In a political sense, conspiracy refers to a group of people united in the goal of subverting established political power structures. This can take the form of usurping or altering them, or even continually illegally profiteering from certain activities in a way that weakens the establishment with help from various political authorities. Depending on the circumstances, a conspiracy may also be a crime or a civil wrong. The term generally connotes, or implies, wrongdoing or illegality on the part of the conspirators, as it is commonly believed that people would not need to conspire to engage in activities that were lawful and ethical, or to which no one would object.

विधि के सन्दर्भ में, षड्यन्त्र का सामान्य अर्थ साज़िश, धोखा देने की योजना, दुरभिसन्धि, गुप्तरूप से की जाने वाली कार्रवाई आदि के रूप में लिया जाता है।

भारतीय दण्ड संहिता की धारा 120-क के अनुसार आपराधिक षड्यन्त्र की परिभाषा