The One Direction star lifted the lid on his past relationships on an episode of the "Zach Sang Show" ... and, when asked about his definition of love, ZM says it's hard for him to answer the question -- 'cause he's not convinced he's actually ever been head over heels.

Malik goes on to say he loves his daughter with Gigi, Khai ... but, she's family and that's a very different kind of love -- so, he doesn't think he's loved outside of family members before.

Worth noting ... at a different point in the interview -- Zayn discusses his song "How It Feels?" and acknowledges it's about not being able to tell a person you're "in love with" you can't be the best version of yourself.

So, on its face, it feels like the guy's a little all over the place about his feelings ... and perhaps not using the best words to describe them. In any case, he said what he said.

Now, it doesn't seem like Zayn's purposely trying to take a shot at Gigi here ... but, the comment's sure to raise fans' eyebrows -- because the two famously dated on and off for about half a decade -- and again, they share Khai, so many assumed he loved Hadid.

Of course, Zayn and Gigi officially broke up (for good) in 2021 ... and, it didn't end particularly well, so it's not out of the realm of possibility that he is, in fact, firing off a shot at his ex.

With that said, Zayn and Gigi have kept their relationship pretty amicable recently ... with Gigi supporting Malik on IG last year and talking about their co-parenting habits positively too.