when you're recording a video or taking a photo of an animal and they walk up to the camera, sniffing it and covering the screen with their face. in most cases, this is used in reference to a pet cat, but it may also be used for other animals and pets, such as dogs.
word may be used as a verb or a noun.
"I was taking a video of my cat and he did a pensis! It was so adorable!
"That pensis of my cat is so goofy. I love it."