on paper; in writing; in the newspapers
Refers to something appearing in a written medium: a newspaper, letter, document, or theoretical plan. Often used in contrast to actual implementation or spoken word.
His proposal looks perfect on paper, but it's hard to implement.
The incident was widely reported in the next day's newspapers.
They announced information about the new product in the press.
The scandal made headlines in the papers day after day.
口頭 means 'orally, verbally,' the direct opposite of 紙上's 'in writing, in print.'
誌上 and 紙上 are pronounced identically but 誌上 refers specifically to appearing in the pages of a magazine, whereas 紙上 refers more broadly to newspapers or written documents in general.
Compound of 紙 (paper) and 上 (on/above), literally 'on paper'. The meaning extends naturally to written media and theoretical plans.