Certain, sure, or reliable; something that can be regarded as definite or dependable.
彼が合格するのは確実だ。
It is certain that he will pass.
この方法は確実な効果が期待できる。
This method can be expected to have reliable effects.
資料を確認した上で、確実に報告します。
After checking the materials, I will report for sure.