Margin
noun, の adjective
If you write outside the columns in your notebook paper you're actually writing in the margins. It's a good space to put doodles.
らんがい
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
サインが欄外にはみ出てしまったんですが、大丈夫でしょうか。
I wonder if it’s okay that my signature is going out of the margins.