One Book
One Volume
noun
When you have one books you really just have one book.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well. The 一 portion gets shortened to いっ as it often is.
このマンガは一冊四百八十円です。
This manga costs 480 yen for one volume.
これは、世界に一冊しかない絵本です。
Only one copy of this particular picture book exists in the world.
あなたのために旅の間に読める本を一冊買っておいたの。タイトルは『地図』よ。
I bought you a book to read during your trip. The title is "Map."