please tell me the meaning and the origin of the expression
"Now is the Winter of our discontent" is a line from Richard III, by Shakespeare. This means that the time of unhappiness will soon end.

Summer of discontent may mean that unhappiness is at its highest.
From http://volokh.powerblogs.com/posts/1111601690.shtml#1571

Another Shakespeare quote, this from Richard II's opening lines: "Now is the winter of our discontent" is often used to describe current times as bad times, in particular a rough winter. But the fuller quote reveals that the bad times are over: "Now is the winter of our discontent/ Made glorious summer by this son of York; / And all the clouds that lour'd upon our homes / In the deep bosom of the ocean buried." In context, the winter of discontent is in the past and has been transformed into a glorious summer, with dark clouds buried in the ocean.

Moreover, you could argue that this counts as a double reverse misleading quote, for as Richard goes on he explains that although these are happy, celebratory times for his fellow members of the House of York, he does not personally share their joy and the "glorious summer."

Apparently it the original phrase Shakespeare quoted was "the winter of discontent."

I guess the summer of discontent just means you've had a dissapointing summer. I think people say this since usually summer is the time when people have a high expection of something good happening, especially related to love and romance.
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Shakespeare's phrase "winter of discontent" is often applied by British journalists to the winter of 1978/9, when a number of British unions called their members out on strikes. This led to the defeat of the Callaghan government in 1979.

It's quite possible that a journalist would use "summer of discontent" to mean a similar period of unrest during the summer months – in allusion to the 78/79 cliché, rather than Shakespeare.

The phrase "winter of discontent" is Shakespearean, as others have noted before me. I believe the Rev. Dr. Martin Luther King, Jr., the great American preacher and civil rights activist, was the first to turn this on its head. In the summer of 1963, King gave a famous speech (the "I have a dream" speech) in Washington, D.C., and in that speech he spoke of the black man's "summer of legitimate discontent."

"The summer of discontent" then itself entered the English language as a phrase to mean a time of discontentment and agitation that is LITERALLY in the summer. We still use "the winter of discontent" to refer to such a time more metaphorically, since "winter" has connotations of darkness and coldness, both of which are undesirable.

If there was rioting in November, we might say that time was the "winter of our discontent."

If there was demonstration and depression from the years 1929 to 1934, we might say that time was also "the winter of our discontent."

If there was struggle and national turmoil in April, May, June, and July of 1963, we might say that time was "the summer of our discontent."
I think the guy meant the "summer of discontent" that took place in Hangzhou, China during the government of "the Gang of Four", 1975. I also don't know the details, but it seems that a great number of dissident activities took place in the same area that summer, and so they called it "summer of discontent". Eventually it ended with a local martial law and a change at the top in 1976. Browse or read books, and you should find out the details.

Anyway, the guy asked this in 2005 Emotion: smile
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In his "I Have A Dream" speech delivered 28 August 1963, at the Lincoln Memorial in Washington DC, Martin Luther King alluded to Shakespeare's Richard III when he said: "This sweltering summer of the Negro's legitimate discontent will not pass until there is an invigorating autumn of freedom and equality."
Now is the Winter of our discontent, made glorious summer by this son of York.