Sub-Editor, or just 'Sub' is a work title in publishing. The title is most frequently seen in connection with newspapers and magazines, but websites are also increasingly making use of subs. In the book world, sub-editor is comparable (but not equivalent) to being a copy-editor.
Being a sub-editor is a desk-based profession which is often a 9-to-5 job, but some daily newspapers (especially morning papers) also run late shifts for its subs, to ensure that all copy that goes into the publication is subbed.
The tasks of a sub
The tasks of a sub-editor can be many and varied, and can vary from publication to publication. The key task of a sub is to ensure that all copy that is published is grammatically correct, spelled correctly and adheres to the publication's style guides (also known as the style book in some cases).
Beyond this, the roles of a sub start to vary. On some publications, it is expected that the sub checks all facts in a story: if a name is mentioned, is it spelled correctly? If a place is mentioned, is it identified correctly? Are dates etc reported accurately? If there are ambiguous or potentially damaging quotes are being used in the publication, have they been run past the quotees to ensure that the quotes accurately reflect their opinion? Is there other information available which might benefit the reader?
Finally, a sub might completely re-write a piece submitted by a journalist or reporter, splitting it into several minor pieces, for example, or changing the order of a piece to make it fit better with another story.
On some publications, subs may occasionally take the place of a section editor, so if one traffic incident is a main story, s/he might decide to use wire services or other reports from other journalists to add more stories to a page, to theme a page around a particular topic.
In many newsrooms, sub-editors will also work with the creative department to put the actual copy onto the page, and then cutting the length of the copy down to size to fit the page better. On magazines, subs might do a rough lay-out of the page, which is then designed properly by designers, or the it might work the other way around: The designer uses the photographs and a headline supplied by the sub, then uses dummy copy to lay out the page, whereupon a sub-editor drops in the copy and does a final sub to ensure that the copy fits on the page as intended.
The place of a sub in the hierarchy
In most magazines, sub-editors will be line-managed by an operations editor, who looks after the day-to-day operations of turning pictures and text into ready-produced pages. Specialist publications might use technical editors who double as subs for their specialty fields.
On newspapers, sub-editors can be assigned to specific sections. It's not uncommon, for example, to have a sub-editor with a particular set of skills or knowledge to look after, say, technology or the cinema section of a newspaper. In other - especially smaller - newsrooms, the subs might work directly for a section editor, or be pooled and work for the whole newspaper on an ad hoc basis.
Friction between journos and subs
Journalists traditionally have a strained relationship with the news desk - by which they'll mean the sub-editors - because nobody likes to get their finely crafted copy re-written, hacked into bits, and spewed out in a completely different order. Often, and especially in under-staffed, under-skilled newsrooms, a lack of communication and understanding between the subs and journalists means that hastily written copy is hastily sub-edited, then hastily slapped on a page before getting re-subbed, whereupon the original story might not make much sense anymore.
Generally, there are two schools of thought on how to deal with this animosity: 1) try to gain an understanding for how your work gets subbed, and then submit work which is easier to sub, or 2) don't ever read anything you've written after it has been submitted, because all the hours you spent slaving away over a hot laptop have been reduced to inane drivel by some corporate lackey who has no idea what they are doing.
Me, I'll take option 2 and the paycheck.