という訳(わけ)だthis is why, this means, it is the case that

社員(しゃいん)は電車(でんしゃ)が遅延(ちえん)したから遅刻(ちこく)したという訳(わけ)です。

This means that the employee was late because the train was delayed. {this is why, this means, it is the case that}

私(わたし)は風邪(かぜ)が流行(はや)っているからマスクをしているという訳(わけ)です。

This means that I am wearing a mask because a cold is going around. {this is why, this means, it is the case that}

同僚(どうりょう)１(いち)：「木下(きのした)は？」同僚(どうりょう)２(に)：「具合(ぐあい)が悪(わる)いから帰(かえ)ったという訳(わけ)だ。」

Colleague 1: "What about Kinoshita?" Colleague 2: "It is the case that he went home because he was feeling unwell." {this is why, this means, it is the case that}

独(ひと)り言(ごと)：「商品(しょうひん)が二(に)千(せん)円(えん)で送料(そうりょう)が五(ご)百(ひゃく)円(えん)だから、合計(ごうけい)が二(に)千(せん)五(ご)百(ひゃく)円(えん)という訳(わけ)だ。」

Monologue: "The item is 2000 yen and the shipping fee is 500 yen, so this means the total is 2500 yen." {this is why, this means, it is the case that}

生徒(せいと)：「次(つぎ)のレッスンは木曜日(もくようび)だけど、祝日(しゅくじつ)だからレッスンが無(な)いという訳(わけ)ですね？」

Student: "The next lesson is on Thursday, but this means there's no lesson because it's a holiday, right?" {this is why, this means, it is the case that}