When someone is "passionate" about something, it means that they care a lot and feel strongly about it. That kind of feeling is called "passion".

You can feel "passion for" an idea, asubject area, or a social cause:

I can tell that you have a real passion for photography.

You can also feel "passion" for a person:

My passion for you knows no limits.

When you use "passion" to talk about romantic love, it sounds poetic.