In the context of the canon story it means nothing anymore. Canon Naruto promised Sakura that he would bring "Sasuke" back for her no matter what. It was then later retconed that Naruto was going to "bring Sasuke back" whether Sakura wanted him to or not, and that "he hated people who lied to themselves".
In the end it really didn't have much of a feeling because quoting from The Last movie "You (Naruto) loved me (Sakura) because of rivalry with Sasuke right?"
In other words in order to justify the canon couple endings multiple aspects of the main story had to be radically shifted. From Sasuke never being "bad" and always "loving everyone" to the POAL not really mattering to the story, and in the end just being something Naruto said.
If your asking what it originally meant then her it is: It was a promise from a young man toward a young woman who's love he wanted, not knowing if he could bring her happiness himself he instead swore to her that he would bring back the person who could bring her happiness (Sasuke). Now in the hands of a person who has any skills as a writer at all, this "the female character loves the abussive bad guy" story would have ended up with the two best friends (Naruto and Sakura) going from strangers---co workers---- friends----- best friend--- bf/gf--- lovers-- husband/wife-- soulmates.
Honestly had Sasuke even been saved, I would have originally planned something like this to happen.
*Sakura sits in her wedding dress crying looking into a mirror, well Ino and her Mother are behind her.*
Ino: What is it forehead girl? Sasuke is out there waiting for you....
Sakura: *tears in her eyes* I know! I know!!!
Mebuki: Sakura seriously... what is it... I know when you cry happily and this isn't it what is wrong?
*Sakura looks around tears still in her eyes.*
Sakura: Wrong? Nothing! How could it be? This is what I've always wanted. I've always begged for this day to happen I've fantasized about it, dreamed about it. What could be wrong? *Tears rolling down her eyes*
Ino: Well instead of bragging about how you won Sasuke from me your sitting her in tears looking at that picture of you and the rest of Team 7.
Sakura: It's nothing. I've always wanted this. It will be just me and Sasuke no one else. Just me and him forever and our kids.... *keeps crying harder.*
Mebuki: Sakura if you don't want to do this you don't have to you know?
Sakura: Why wouldn't I want too? The whole village is here, and there are some other people here from other village to support me... why wouldn't I do it? I've always wanted too...
Mebuki: They don't matter... this is your life. What do you want in your heart?
Sakura: I know what I want! I've always wanted him!
Ino: Are you sure?
Sakura: Of course!! Since we were little girls I'd sit and look into a mirror like this one and say it... *wipes tears from face.*
Mebuki: Then say it.
Sakura: Yeah.. from now on my name will be Sakura Uchiha... They will call me....*starts crying again* Sakura Haruno Uchiha *cries harder* Sakura Uchiha Haruno *keeps crying then pauses* I'll be... I'll be... *starts crying hard again*
Ino: .....
Mebuki: Your going to be?
Sakura: *takes a deep breath well tears roll down her face, looks at the image of Team 7 for a second then says.* Sakura.... Haruno... Uzumaki... *stops crying for a minute in shock*