expression
Used to introduce a concise summary or conclusion, often at the beginning of a sentence. Slightly more formal than 要するに.
手短に言えば、その計画は失敗だった。
In short, the plan was a failure.
手短に言えば、彼は賛成していない。
To put it briefly, he doesn't agree.
つまり is a very common and neutral way to say 'in other words' or 'that is to say'. 手短に言えば explicitly emphasizes brevity.
Composed of 手短に (briefly, concisely) + 言えば (conditional form of 言う, 'to say'). The phrase literally means 'if said briefly' and functions as a set expression.