The silly season is the period lasting for a few months (starting in mid- to late summer) in the United States, the United Kingdom and Australia typified by the emergence of frivolous news stories in the media. This term was known by the end of the 19th century and listed in the second edition of Brewer's Dictionary of Phrase and Fable and remains in use at the start of the 21st century. The fifteenth edition of Brewer's expands on the second, defining the silly season as "the part of the year when Parliament and the Law Courts are not sitting (about August and September)".
Typically, the latter half of the summer is slow in terms of newsworthy events. Historically, newspapers (which rely on subscriptions) see a drop-off in readership during this time. In the UK, Parliament takes its summer recess, so that parliamentary debates and Prime Minister's Questions, which generate much news footage, do not take place. In order to retain (and attract) subscribers, newspapers would print attention-grabbing headlines and articles to boost sales, often to do with minor moral panics or child abductions. Other countries have compareable periods, e.g. the "Sommerloch" in Germany.
A side effect of stirring up the public in this manner comes when an authentic story is dismissed as a prank, or when a superfluous story is taken as legitimate (eg: The Sun, The National Enquirer etc). Source.