[In awe of TV]

This is only my opinion, others will have their own definition.

what is it?
It's difficult to define, but I think it's an attraction and I don't mean looks. It's a bunch of things - could be the tone of voice, a nice smile, a certain gentleness and/or kindness, the cologne he's wearing, his eagerness to get to know you, common interests, his sense of humor, the respect he shows for you and last but not least - it's a gut feeling. I would have to feel and/or receive a comfort feeling, someone I want to spend time with. So much more to list, but these are the important signs. There another sign, but I would have to take this offline and pm it to you!

how do you know when it's there or not there?
I can sense chemistry within the first 5 minutes of meeting someone. If I felt chemistry with someone, I will want to continue talking and getting to know him more and flirt. Flirting is huge if I'm feeling chemistry. No chemistry, no flirting. I will remain cordial through the date, say good night, thank him for a nice evening and move on. Definitely no kiss.

how much does it mean for predicting a long term relationship?
It doesn't predict a long term relationship. It only means he's right for now. Long term would require a background check. ; )

can it be absent at various stages of relationship?
No, it's can't be absent for me.

can chemistry grow or is it either there or not there?
It's either there or not. If it's there, it can definitely grow.

Can a relationship exist on and on without it?
Nope, not for me. If I don't feel any chemistry, he could definitely remain a in a friend relationship, but nothing more. If I were to consider a relationship, there would have to be romance and I couldn't be romantic with someone I don't have chemistry with. I would rather be home with my dog that be with someone who I am uncomfortable with.

I'm anxious to read other people's definition . . .