Why thank you for asking SL!
I see it as a balance, a harmony of your own senses. So that can be expressed in quite a few different ways, it depends more on the why:
In health: having your body fit and healthy usually keeps your mind healthy as well. So, you feel like your body and mind are at harmony, as opposed to , you know, constantly uncomfertable or stressed & sick (stuff I actively try to get away from ALL the time)
In cooking: Can not only crate a harmony of helping your own health, but can create a direct link between a skillset (ie, cooking your own veggies) and that health.
Relating to people: I like to just keep good relations with people mostly because stressed feelings tend to stress me out, and like I said stress can effect my body, which can make me feel unhealthy which I'd actively want to stay away from. (See, it's all connected
)
I just picked the stuff most people always tend to bring up (health, diet, etc).
It's basically keeping everything in your life that you care about in harmony, balance (Whatever that means to you). That's the core of Si, to me.