Incomplete
Imperfect
noun, な adjective
You know that 完全 means "complete" or "perfect." So, a not "complete" or "perfect" is something that is incomplete or imperfect.
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. It also will help if you can read 完全.
不完全な人間
an imperfect human being
不完全なデータ
incomplete data
不完全な形
an incomplete form
人間はみんな不完全です。
Everyone is imperfect.
完全なものよりも不完全なものの方が人情味があってよくない？
Aren't incomplete things better than complete things, since they have a humanness about them?
勝ち試合が雨で中止になり、トーフグソフトボールチームのシーズンが不完全に終わった。
The Tofugu softball team had an incomplete end to their season when the game they were winning was suspended due to rain.