Definition of "butterflies"

I was apprehensive, feeling butterflies, pissed, the sun cracking the flags.

2005, Andrew Porter, Suicide Squad: The Inside Story of a Football Firm

I should be over all the butterflies / But I'm into you

2013, Hayley Williams, Taylor York (lyrics and music), “Still Into You”, in Paramore, performed by Paramore

Attraction depends on several factors, including mystery and spontaneity—especially early on in the relationship. It’s what keeps those butterflies and the desire for more connection alive.

2023 August 22, Megan Schaltegger, “Hate to Say It: The "Find My" App Could Be Hurting Your Relationship”, in Cosmopolitan‎