Portion
Section, Part
noun
Part of a part? That's a portion, a section of that part, and even a part in itself!
ぶぶん
This is a jukugo word, which usually means on'yomi readings from the kanji. As long as you know the readings for these kanji, you should be able to read this word just fine.
この部分は、何色にしますか？
What color do you want for this part?
のうの前の部分の名前って何だっけ？
What was the front part of the brain again?
この映画、共感出来る部分だらけでめちゃくちゃ泣けた。
The movie was full of parts I sympathized with and I cried all over myself.