The word criminal Conspiracy is belong to the INDIAN PENAL CODE 1872.
The IPC defines criminal conspiracy as follows;
https://www.indiacode.nic.in/show-data?actid=AC_CEN_5_23_00037_186045_1523266765688&orderno=126
Section120A
According to the Section 120A of IPC, When two or more people agree to do or cause to be done-
(a) an illegal act
(b) An act which is not illegal by illegal means, such an agreement is designated a criminal conspiracy; provide that no agreement except an agreement to commit an offence shall amount to a criminal conspiracy unless someone act beside the agreement is done by one or more parties to such agreement in pursuance thereof.
Explanation :
It is immaterial whether the illegal act is the ultimate object of such agreement, or it is merely incidental to that object.
so in this section, if a person doing any act which is illegal or harms the person knowing about the facts that doing that harms the person is said to be a criminal conspiracy.
The next one is SECTION 120B which defines the punishment related to the criminal conspiracy.
According to the SECTION 120B
(a) Whosever is a party to a criminal conspiracy to commit an offence punishable to death, imprisonment of life for a term of two years or upward shall, whether no express provision is made in this code for the punishment of such conspiracy be punished in the same manner as if he has abetted such offence.
(b) Whoever is a party to a criminal conspiracy other than a criminal conspiracy to commit an offence punishable as aforesaid shall be punished with imprisonment of either description for a term not exceeding six months, or with fine or with both.
Both the section defines the word criminal conspiracy and it has a very deep meaning in the IPC.
The criminal conspiracy and the joint liability work together because the criminal liability comes together by both parties.