A continuous sequence or a series without breaks; things that are contiguous or connected (e.g., rooms that are connected).
その部屋は廊下と一続きになっている。
That room is continuous with the corridor.
山並みが一続きに見え、遠くまで同じ風景が広がっていた。
The mountain ranges looked continuous, the same scenery stretched far away.
この企画は一続きの問題として扱われているため、別々に処理できない。
This project is treated as a continuous set of problems, so they cannot be handled separately.