1'For that reason' or 'therefore' — a connective expression that presents what follows as the result of what was just stated. Slightly more formal than だから and common in both speech and writing.
事故で道路が封鎖された。そのため、電車で行くことにした。
The road was closed due to an accident. For that reason, I decided to go by train.
彼は病気がちだった。そのため、会社を辞めることになった。
He was often ill. As a result, he ended up quitting his job.
今年は雨が少なかった。そのため、野菜の値段が上がっている。
There was little rain this year. Because of that, vegetable prices are going up.
この地域は高齢化が進んでいる。そのため、医療の充実が急がれている。
The population in this area is aging. For that reason, improving healthcare has become an urgent priority.