The act of cuddling and other such public displays of affection (PDA) in an open area. Nesting is commonly done spontaneously with someone you don't particularly know very well.
Group nesting is called a Nest Fest.
This act can lead to Burrowing. Burrowing can lead to babies.
Joel - "Eli went off to nest with that girl again."
Sam- "What a nesting whore."