It gets blurred and means different things to different people but the basic idea is the one who 'receives' pleasure in sex (for cis straight relationships, the default is the woman, for (also cis) gay men the one being penetrated, and then for (again cis for brevity) lesbians the one doing the 'work' such as fingering), commonly paired with submissiveness and often conflated as being the same thing. They were originally terms exclusively used by gay men but eventually found adoption outside of that even though top/bottom roles are so often far less strictly defined, adhered to, or even identifiable in other queer relationships than that. In my personal experience though most people talking about being a bottom online are primarily referring to submissiveness instead.
Nobody memes the power bottoms :(
I don't get it 😅 Am I supposed to look for something not obvious at first glance in the image? I'm not seeing anything