1A noun meaning the whole or entirety; refers to the whole as a single unit rather than individual parts (used as in 'as a whole' or 'the whole of ~').
会社全体で売上が伸びた。
Sales increased across the whole company.
全体の構造を理解する必要がある。
You need to understand the overall structure.
その問題は全体の一部に過ぎない。
That problem is only part of the whole.
2Used adverbially to mean 'as a whole' or 'in the first place' (phrases like '全体として' are common).
全体として見れば、計画は成功だ。
Viewed as a whole, the plan is a success.
全体の流れを把握してから細部に入ろう。
Let's grasp the overall flow before getting into details.
3Used (often in the phrase '一体全体') to intensify questions or exclamations, meaning 'on earth' / 'in the world' / 'the heck' (e.g. 'what on earth?').
一体全体、彼はどこに行ったんだ？
Where on earth did he go?
一体全体どうしてこんなことに？
How on earth did this happen?