What's a short, snappy way of explaining why feminism is important?

I once saw a button that said, "Feminism is the radical notion that women are people" and thought that was a good way to put it.
Edit: Whoops. Did not know this was a women-only space; I'll see myself out.
- I love this one! It's short, snappy, and cuts to the simple matter that despite all of the complexities surrounding feminism this is essentially what it's about.
- "women are people" is not the worst reduction of feminism though, it's not snark even if some might not realize feminism is essentially connected to the idea that women are people like men, essentially just an extension of the Enlightenment's egalitarian ethos of equal rights for humanity being extended to women, which could be re-articulated or simplified just as "women are people"
  Also, this is a women's-only community, I don't think you're supposed to post here 😅

Short and snappy: Because men are still the default and that doesn't make any sense when about half of humanity are women.
Some examples: Medicine, crash tests, design (size of things), movies (see the Bechdel Test for a bar that was put on the ground that is still not cleared surprisingly often) and other media. This list goes on and on.
- This is excellent! You're right, women are an afterthought at best, we're often not included in academic research, policies don't think of us, and we're underrepresented in key places. Humanity should be the default!

I would say, that feminism boils down to "the fight to overcome oppressive gender stereotypes and gender based discrimination". Concrete this means, that feminism aims at allowing everyone, regardless of their gender or identity, to truly express themselves. This means, that men are allowed to cry, that women are not always seen as someone to potentially date, but it also means, that in the medical field women are more represented in studys. Feminism aims at creating an equal world for everyone where everyone can express themselves.

Feminism is not anti-male (although misogynists act like it is). Feminism is fairness.
I think this is a common, fundamental misunderstanding that many people have.

When the rights of half your population are at risk, everyone is at risk.
- Yes! We're in nearly every home, we're half the population ffs

We earn less, do more chores, are frighteningly objectified and are at greater risk of domestic/sexual abuse. And nobody is going to stop that unless we kick off about it.

Because women/girls deserve equal rights, opportunities, and representation. We are 50% of the population but men are so often considered the default human and in many positions are taken more seriously than women, even if the women are far more qualified

Are women human, are they people? If yes, why should they have fewer rights than men? If all humans are created equal, women and men should all share and enjoy the same rights.
- That's a good one! It's an ELI5 version which is great

To me, feminism isn't about the raising up of women to be equal to men, it's about the raising up of femininity to be equal to masculinity, so we can all access a full range of human expression.
- yeah, ironically femmephobia seems common among self-described feminist women, as though the way to be a good feminist is to shed femininity as chains. (Unfortunately I was one of those femmephobic feminists, for a period - Julia Serano is who cured me of that.)
  though I certainly wouldn't want to call feminism just the process of making femininity equal to masculinity (reproductive rights after all are feminist but not about femininity), I think it's important to call out the need for taking femininity seriously as a part of feminism
  
  You are totally right, its not an all-encompassing definition. It is a good sound-bite, especially for people who feel like they don't benefit (or even lose something) from feminism.

I want to add that it's not just the idea of equality, it's also an analytical framework and a social movement. Feminism includes ways to understand patriarchal systems, as well as methods of dismantling them.

Feminism fundamentally benefits eveyone by tearing down gender norms and building towards a brighter future.
Thats how I would describe it to anyone, especially men