The world of publishing and printing has its own language, and many of the words that arose from the mechanical printing methods of the 1950s and earlier are familiar to anyone who uses a word-processing programme, or desk-top publishing software.
The sort of printing that went on in the days when Lexie was working at the Elsewhere offices was probably letterpress printing, although the 1950s were a decade when this method which had been established for hundreds of years began to change. This was necessary in order to find a cheaper way to print newspapers and magazines, and maybe this is one of the reasons Elsewhere doesn't make Innes any money in the novel. Over the late 50s and early 60s, the printing industry moved towards using offset printing combined with photocomposition.
Certainly words such as set and justified come from the traditional methods of composing type using a composing stick. Although this was certainly a laborious process, there are many who consider it to have been very artistic, and that it created much more aesthetically pleasing pages of print than the more automated electronic methods used in word-processing programs today are capable of. The video on this page indicates what a detailed task it was.
A galley would hold the type in place before printing.