Extremely hot (piping hot, scalding) — often written in kana; also can be written as 熱々.
熱々のスープを火傷しないように気を付けて飲んでください。
Be careful not to burn yourself when drinking the piping hot soup.
焼きたてのパンは熱々で香りがいい。
Freshly baked bread is piping hot and smells great.
鍋料理はあつあつを皆で取り分けて食べるのが楽しい。
It's fun to share and eat hot hot hot-pot dishes together.
Passionately in love; a couple being very affectionate and lovey-dovey.
新婚の二人はいつもあつあつで見る人がうらやましい。
The newlyweds are always lovey-dovey — it's enviable to see them.
彼らはあつあつでレストランでも手を離さない。
They're so in love they don't let go of each other's hands even in restaurants.
あの二人はあつあつで周りが見えないみたいだ。
Those two are so into each other they seem unaware of everyone else.