This is a two part question.
1.) When spelling out a word in kana, what is the correct way to call the small つ (for example the small っ in ちっちゃい)?
I only have experience with my Japanese friends using the informal sounding
Is there a formal grammatical term for this "character"?
2.) If there is, but in reality it sounds too academic, which term would be the most immediately understandable in an informal setting?