Subspace log

A subspace log was a log of incoming and outgoing subspace communications. In Federation starships of the mid-23rd century, this log was periodically filed by a ship's communications officer.

In 2266, after Lieutenant Nyota Uhura, the communications officer aboard the USS Enterprise (NCC-1701), had filed a subspace log, her supervising officer, Lieutenant Commander Spock, informed her that there was an error in the frequencies column. 

When Ro Laren was confronted by Jean-Luc Picard about leave the USS Enterprise (NCC-1701-D) without authorization, in 2368, she told him that she had actually gotten permission via communication from Admiral Kennelly, which she said could be confirmed by the subspace log. 

Later that year, Data and Spock, who had hacked into the Romulan Information Net, were able to access Romulan subspace logs that identified a transmission from the Romulan surface to a Barolian freighter near Galorndon Core, which simply contained a short sequence of numbers: 1400. 

In 2369 Constable Odo checked all of the communication logs during the Klaestron Civil War and found evidence that Curzon Dax and Enina Tandro had an affair.