説明が

explanation

→ 説明
phrase Uncommon #15,619
explanation 説明 means “explanation” or “説明”; が marks it as the subject. It commonly appears in expressions such as 説明ができる (can explain) and 説明が上手 (good at explaining).
JA: この問題は説明が難しいです。
EN: This problem is difficult to explain.

パパこの人説明が本当に上手なのよ

Daddy, this person is really good at explaining things.

— きっと、うまくいく (2009)

なぜ彼女が学校を休んだのか説明ができません

I can't explain why she was absent from school.

ほかの条件同じなら一番簡単な説明が一番よい

All else being equal, the simplest explanation is the best.

彼は自分の行為について責任ある説明ができるか

Can he give a responsible account of his actions?

説明が最高です

The explanation is excellent.

— ビッグ・シック ぼくたちの大いなる目ざめ (2017)

それで説明がつく

That explains it.

説明がつかないあざ出血はありますか

Do you have any unexplained bruising or bleeding?

同じ説明がその場合にもあてはまる

The same explanation applies in that case as well.