Stepping stone - Tradução em português

O que significa 'stepping stone" em português?

Eu ouvi a música da Duffy e não entendi.

I rememeber way back way back when
I said I never wanna see your face again
Cause you were loving yes you were loving somebody else
And I knew oh yes I knew I couldnt control myself
And now they bring you back into my life again
And so I put on a face just like your friends
But I think you know oh yes you know what's going on
Cause the feelings in me oh yes in me are burning strong

[Chorus]

But I will never be your stepping stone
Take it all or leave me alone
I will never be your stepping stone
I'm standing upright on my own