Something that is natural, reasonable, or obvious — commonly used in speech; often written in kana.
そんなに驚くことじゃないよ。できるのが当たり前だ。
There's nothing to be so surprised about. It's only natural that you can do it.
彼が忙しいのは当たり前だ、あれだけ仕事を任されているのだから。
It's natural that he's busy — he's been entrusted with so much work.
挨拶をするのは社会人として当たり前のことだ。
Greeting people is an expected courtesy as a member of society.
Usual; common; ordinary — indicating what is normal or the prevailing standard.
ここでは英語が話せるのが当たり前ではない。
Here, it's not taken for granted that people can speak English.
若い世代はスマホを持っているのが当たり前になった。
It's become normal for younger generations to own smartphones.
当たり前のことを確認するだけでは問題は解決しない。
Just confirming the obvious won't solve the problem.