The title of a viscount may be either a placename, or a surname, or, as is more often the case, a combinations thereof. In any event, the style of a viscount is "The Viscount X," or "The Viscount X of Y." Examples include: The Viscount Falmouth (placename); The Viscount Hardinge (surname); The Viscount Gage of Castle Island (surname of placename); and The Viscount Combermere of Bhurtpore (placename of placename). An exception exists for Viscounts in the peerage of Scotland, who are styled "The Viscount of X," as in: The Viscount of Arbuthnott (surname).
Normally, The Viscount X is known as Lord X, while his wife is Lady X. (X is only the main title: the Viscount of Arbuthnott would be Lord Arbuthnott; the Viscount Gage of Castle Island would be Lord Gage.) The children of a viscount are known as "The Honourable [Forename] [Surname]".
The word derives from the Latin vice comes which was the rank of a deputy to a count.
The same or a similar rank exists in other monarchies.