Declassified indicates that some form of intelligence or information has been thouroughly vetted by an authority that has oversight of the topic and has cleared it for public viewing.
There are times that this means a document, for example, has been cleared as to not divulge information useful to foreign entities or those who would use it to harm the releasing country or government. This can also be accomplished by redacting any sections that remain classified and releasing the information.
Most documents will have the former classification redacted by a black bar over the classification level and will have the word DECLASSIFIED stamped onto every page.
Iron Noder 2017