A phrase used to summarize or state something briefly — equivalent to “in a word” or “to put it briefly.”
一言で言うと、このアプリは使いやすい。
In a word, this app is easy to use.
長い説明の後で、一言で言うと彼の提案は現実的ではないという結論になった。
After a long explanation, in a word the conclusion was that his proposal wasn't practical.
一言で言うと、準備不足だった。それが失敗の原因だ。
To put it briefly, we were underprepared. That's why we failed.