The act of running to a person and hugging them tightly with enthusiasm, followed immediately by rubbing or burrowing one's face into the recipient's neck or face.
This is usually done out of love or greeting, to express emotion and fondness.
Friend 1: Sorry about that, I didn't mean to take so long.
Friend 2: *fruffles* I missed you! Where have you been!?
Best Exemplified in the movie Ponyo, when Ponyo is reunited with Sosuke in her human form.