Ask single men or women the definition of "chemistry" and they'll usually say it's an instantaneous mutual physical attraction--feeling drawn to or warm toward someone. And they'll say it's mostly about that person's looks. Either the person is visually appealing to them or not.
I'm not so sure. My experience in over 40 years of dating and relationships, as well as studies done by social scientists, psychologists, and other experts I read, show that chemistry is about much more than a sexual "spark."
Webster's dictionary defines it as "a strong mutual attraction, attachment, or sympathy" (sympathy meaning an inclination to think or feel alike). Notice there's no mention of physical appearance. The true definition of chemistry involves two humans having similar thoughts and feelings, what I would call "a meeting of the minds and hearts." It's not just a physical reaction in your body or libido but about the impact that your heart and mind have on the body.
Think about this example: Haven't you, like me, had experiences where you weren't initially attracted to someone's body type but then noticed the flame of desire after he took your hand? Or you found yourself warming up to the person once you got talking? You agreed with his ideas and felt a kinship. He told you of his heartbreaks, and you empathized. He made you laugh, and you were compelled to hug him. He made great eye contact with you as you spoke, and you felt a really cool connection. It's hard to explain, but it happens naturally and organically and sometimes surprisingly as we share more conversation and laughter with other people...when we open up and reveal fears, insecurities, and other usually hidden truths.
You know how great it is, right? When you're invited and welcomed into someone's inner world and begin to feel a sense of belonging, like you're looking into a mirror and having your own thoughts and feelings reflected back? And soon you see that person (who initially wasn't your physical "type") with brand new eyes and in a whole new way.
They say the eyes are the "windows to the soul." So, if you're looking for a soulful connection with someone that's more than just skin deep, I recommend giving a fellow human the gift of eye contact. Listen with your heart. Notice the ways your minds mesh and the commonality of the wavelength you're each on. And then be open to the possibility of sparks flying. Don't overthink it or have any expectations. Let your heart lead the way.