#ParisAttacks, #LoveWins, #elxn42: The essential hashtags of 2015

From the Canadian election to the Paris terrorist attacks to the incredible photos beamed to Earth during the Pluto flyby, social media remained, for yet another year, the way many people followed news as it unfolded.

Twitter's end-of-year report includes some of the most popular hashtags and topics that resonated with the more than 300 million users of the social media service. 

#ParisAttacks

Paris endured two sets of attacks by terrorist gunmen 10 months apart this year. 

The attack on the Paris office of satirical magazine Charlie Hebdo in January left two police officers and 10 journalists dead. Five others were killed in shootings days later. 

That day, the hashtag #JeSuisCharlie — French for "I am Charlie" — was trending in France, Canada and the U.K., with more than 130,000 mentions on Twitter.

Political cartoonists posted their drawn reactions to the deaths at the magazine, many of them using the hashtag #CharlieHebdo. 

In November, a series of co-ordinated attacks in Paris killed 130 people. Dramatic video and photos from the attacks were shared on social media, and people on Twitter began to use the hashtag #PrayForParis, although others said #PrayForWorld would be more appropriate, in light of other attacks elsewhere. 

During the attacks, Parisians used the hashtag #porteouverte, "open door," to offer shelter to people stranded in the streets. 

When a French police dog died during a raid days after the attack people used the hashtag #JeSuisChien to pay tribute on Twitter. 

#BlackLivesMatter 

Social media is the tool of choice for a new civil rights and social movement in reaction to police killings of black youth in Ferguson, Missouri; Baltimore; Charleston, S.C.; Cleveland and elsewhere, represented by the hashtag #BlackLivesMatter. 

• Black Lives Matter: A history in photos

It originated on Twitter in November 2014 when it was announced that a grand jury in Ferguson had declined to indict Darren Wilson, the officer who had shot and killed Michael Brown in Ferguson following a confrontation. 

Since then, #BlackLivesMatter has become a worldwide rallying cry. 

• Black Lives Matter is mouthy, offensive — and spot on: Neil Macdonald

Twitter counted #SandraBland among the top 10 trending news hashtags of 2015. Brand was found dead in a Texas jail cell in July. She'd been arrested three days earlier, after being pulled over for a traffic violation. Authorities say Bland hanged herself, but her family have questioned that finding. 

#elxn42

Canada's 42nd general election followed an 11-week campaign that saw several hashtags being established to comment on various scandal and policy announcements. 

In September, it was revealed that Conservative candidate Jerry Bance had been caught on hidden camera urinating into a coffee mug during a house call to repair a leaky sink when he worked as a service technician in 2012.

The Conservatives dropped him and the hashtag #peegate was born. 

During the Globe and Mail leaders' debate, Stephen Harper said that he would "bring in more" refugees than in the past, but that "we do not offer them a better health-care plan than the ordinary Canadian can receive. I think that's something that new and old stock Canadians can agree with."

That phrase became a hashtag, #OldStockCanadians, where some called it a "dog whistle" message to the Conservative base. Frank Graves, president of EKOS Research, agreed. 

"It's part of the deliberate strategy to sort Harper's constituency from the rest of the electorate," Graves told CBC Montreal's Daybreak. "It creates a sense of us versus others."

In October, the Conservatives pledged to establish a tip line for reporting "barbaric cultural practices" to the RCMP. 

Kellie Leitch, a Conservative candidate and the labour minister and minister for the status of women in the Harper government, tweeted ahead of the announcement with the hashtag #BarbaricCulturalPractices.

But critics of the plan latched onto the hashtag to condemn what they saw as Canada's truly barbaric cultural practices. 

#LoveWins 

After the U.S. Supreme Court extended the right to marry to same-sex couples across America, politicians posted their reactions to Twitter.

President Barack Obama tweeted his reaction with the hashtag #LoveWins, which topped the Twitter trends that day in the U.S. and Canada. 

#PlutoFlyby 

In July, NASA confirmed that its New Horizons spacecraft successfully completed a flyby of Pluto, culminating an epic journey from Earth that took 9½ years and spanned more than 4.8 billion kilometres.

What followed were dazzling high-res photos of Pluto's surface, its atmosphere and its moons. 

#IStandWithAhmed 

In September, a 14-year-old Texas boy, Ahmed Mohamed, was arrested and taken to juvenile detention after teachers mistook the homemade electronic clock he had brought to school for a bomb. 

The hashtag #IStandWithAhmed emerged for people who felt the teen had been treated unfairly because of his race, religion and name. 

Ahmed's story crossed the desks of some of the most powerful people in the U.S., and he was inundated with messages of support and offers to visit the White House, the MIT astrophysics facility and the Facebook campus. 

#CaitlynJenner 

Sometimes, events on social media themselves become news. When Caitlyn Jenner appeared on the cover of Vanity Fair in June with her new identity and new name, she also launched her Twitter account. 

She gained a million followers in just over four hours, breaking the previous record held by Barack Obama.