Why are celebrities all tweeting about this?

Hugh Jackman showing his support. Source: Instagram

FROM Hugh Jackman to Oprah to LeBron to Gwyneth, everyone seems to be tweeting their support for #LeanInTogether. So what's it all about?

The #LeanInTogether hashtag is part of a new public awareness campaign championed by Facebook COO Sheryl Sandberg.

Sandberg started the Lean In movement two years ago with a book which encouraged women to pursue their ambitions, support each other and resist being held back. #LeanInTogether goes one step further, encouraging men to get involved in supporting gender equality too.

"The conversation about equality has long existed by women, for women, in women's forums where women are, and that will continue, and that's important," Sandberg told CNN.

"But bringing it to the centre of the court, bringing men to the centre of that conversation — people like LeBron James and Steph Curry and Dwayne Wade, saying 'I'm in for equality and here's why' — I think that could be transformative."

With the support of the NBA and the WNBA, the #LeanInTogether campaign uses YouTube, Twitter, Instagram and Facebook, and encourages men to "lean in" for women. It operates on the principles that "Children with involved fathers are happier, healthier, and more successful; Couples that share responsibilities have stronger marriages; Diverse teams and companies produce better results."

LeanInTogether.com has a host of "simple, clear, everyday, practical" pieces advice for men when thinking about gender equality, such as being a 50/50 partner at home, watching what your daughter is watching so you can challenge stereotypes in the media, and giving women the credit they deserve in the workplace.

Its message is clear: "Men, show the world you're in for equality. Women, celebrate men leaning in."