term:

Fault

fault n

[Anglo-French faute lack, failing, ultimately from Latin fallere to deceive, disappoint]
1 : a usually intentional act forbidden by law
;also
: a usually intentional omission to do something (as to exercise due care) required by law see also negligence compare no-fault strict liability at liability NOTE: Sometimes when fault is used in legal contexts it includes negligence, sometimes it is considered synonymous with negligence, and sometimes it is distinguished from negligence. Fault and negligence are the usual bases for liability in the law of torts.
2 : responsibility for an act or omission that causes damage or injury to another [relative degrees of ] see also comparative fault

at fault
: liable or responsible based on fault [was not at fault]

Source: Merriam-Webster's Dictionary of Law ©1996. Merriam-Webster, Incorporated. Published under license with Merriam-Webster, Incorporated.