A plain tiger butterfly sits on the nose of a girl during a photocall to highlight the forthcoming "Sensational Butterflies" exhibition at the Natural History Museum, March 31, 2015, in London. Getty Images

When you see your female friends Tuesday, give 'em high-fives: It's International Day of the Girl.

International Day of the Girl was first recognized in 2011, when the United Nations general assembly voted to set aside Oct. 11 as a day to honor girls and work to improve their lives. It's a day for sharing inspiration and spreading awareness. This year's celebration centers on the theme "Girls' Progress = Goals' Progress: What Counts for Girls."

In the United States, President Barack Obama took International Day of the Girl as a moment to shed light on Americans' work to get more young women involved in the historically male-dominated science, technology, engineering and math fields, push for equal pay and campaigns to curb sexual assault on college campuses.

"This is the future we are forging: Where women and girls, no matter what they look like or where they are from, can live free from the fear of violence. A future where all girls know they can hold any job, run any company, and compete in any field," Obama said in a statement. "Let us keep working to build a world that is more just and free — because nothing should stand in the way of strong girls with bold dreams."

International Day of the Girl is about more than just girl power — it's about redoubling global efforts to improve their lives. In some countries, the situation is bleak.

There are 31 million school-aged girls who don't have the opportunity to attend elementary school. About 35 percent of women across the world have encountered physical or sexual violence. More than 90 percent of teenaged girls have said they wish they could alter the way they looked. Only 4 percent of the top U.S. companies have women as their chief executive officers.

On International Day of the Girl, start a discussion about the challenges facing young women. Then, as you celebrate them, share these quotes from famous females, collected from Harper's Bazaar, StyleCaster and Goodreads:

"Girl power in my mind is to let girls be exactly what they are. Let them be angry. Let them be resentful. And rebellious. Let them be hard and soft and loving and sad and silly. Let them be wrong. Let them be right. Let them be everything, because they are everything." — Amy Sherman-Palladino

"Women will only have true equality when men share with them the responsibility of bringing up the next generation." — Ruth Bader Ginsburg

"A woman is like a tea bag — you never know how strong she is until she gets in hot water." — Eleanor Roosevelt

"A feminist is anyone who recognizes the equality and full humanity of women and men." — Gloria Steinem

“Women are supposed to be very calm generally: but women feel just as men feel; they need exercise for their faculties, and a field for their efforts as much as their brothers do; they suffer from too rigid a restraint, too absolute a stagnation, precisely as men would suffer, and it is narrow-minded in their more privileged fellow-creatures to say that they ought to confine themselves to making puddings and knitting stockings, to playing on the piano and embroidering bags. It is thoughtless to condemn them, or laugh at them, if they seek to do more or learn more than custom has pronounced necessary for their sex." ― Charlotte Brontë

"It took me quite a long time to develop a voice, and now that I have it, I am not going to be silent." — Madeleine Albright

"Feminism isn't about making women strong. Women are already strong. It's about changing the way the world perceives that strength." — G.D. Anderson

"The most effective way to do it, is to do it." — Amelia Earhart

"Of course I am not worried about intimidating men. The type of man who will be intimidated by me is exactly the type of man I have no interest in." — Chimamanda Ngozi Adichie

"Never limit yourself because of others’ limited imagination; never limit others because of your own limited imagination." — Mae Jemison

"We realize the importance of our voices only when we are silenced." — Malala Yousafzai

"Who runs the world? Girls." ― Beyoncé Knowles