In patent data, a CITATION is a reference to a previous work which is relevant to the current patent application . They can be provided by the applicant, the patent examiner or sometimes third parties (typically during opposition phase).
The list of relevant citations for one patent is included in the search report.
They are documents the examiner is going to look closely at to establish the novelty of the invention
The cited document may be a patent or a non-patent (NPL) publication (e.g. a journal article).
Documents listed in the search report are also called backward citations (since they have been made public before the given patent.
Further applications that will cite the given patent will be addressed as forward citations.
Thus if Patent Z contains in its search report a reference to Patent A, A will be a backward citation for Z and Z a forward citation for A.
Other information that can be retrieved from citations is:
Citation origin: at what phase of patent’s life the reference has been introduced
APP citations introduced by the applicant
SEA citations introduced during search (from Search Report)
ISR citations from the International Search Report
SUP citations from the Supplementary Search Report
PRS "PRe-Search" citations (available before official publication; only for US applications)
EXA citations introduced during examination
OPP citations introduced during opposition (citations by opponent published with a European Patent Specification (EP-B2))
APL citations introduced when filed for appeal by applicant / proprietor / patentee
FOP citations introduced when filed opposition by any third party after the publication of a European Patent Specification (EP- B1)
TPO citations introduced because of Third Party Observations (Art 115 EPC)
CH2 citations introduced during the Chapter 2 phase of the PCT
Citation origin suffers in many cases of an institutional bias in cases, like USPTO, where applicant is required to file all possible prior art for duty of candor.
Application Category: this flag shows out how relevant is the citation regarding the limitation of novelty or claims.
X Particularly relevant if taken alone.
Y Particularly relevant if combined with another document of the same category.
A Defining the state of the art and not prejudicing novelty or inventive step.
O Non-written disclosure.
P Intermediate document.
T Theory or principle underlying the invention.
E Earlier patent application, but published after the filing date of the application searched (potentially conflicting patent documents).
D Document cited in the application.
L Document cited for other reasons.