In finance this term refers to two or more loans, bonds or series of preferred stock having equal rights of payment, i.e., having the same level of seniority. For asset management firms, the term denotes an equal allotment of trades to strategically identical funds or managed accounts.
This term is also often used in bankruptcy proceedings where creditors are said to be paid 'pari passu', or each creditor is paid pro rata in accordance with the amount of his claim. Here its meaning is 'equally and without preference'.
Black's Law Dictionary (8th ed. 2004) defines "pari passu" as "proportionally; at an equal pace; without preference". "Pari passu" refers to equal treatment of the credits against each other with reference to the common security.