Vertical and side (horizontal). That means you have the length and width and the vertical and horizontal.

This is a jukugo word that usually uses the kun'yomi readings of the kanji. You should be able to read this on your own.

Note however, that there is a less-common on'yomi reading, じゅうおう, which is used in some idioms. It's good to know this reading exists, but you probably won't come across it very often.