Completely/fully — deeply immersed (e.g., in liquid) or figuratively totally absorbed/addicted to something. A mimetic adverb.
温泉にどっぷり浸かって疲れを取った。
I soaked fully in the hot spring and relieved my fatigue.
彼は最近仕事にどっぷりはまっていて、休みの日も働いている。
Lately he's totally absorbed in his work and works even on his days off.
小説の世界にどっぷり浸かって、一日中読みふけった。
I was completely immersed in the world of the novel and read all day.
どっぷりと油に漬けて揚げると、風味がよくなる。
If you deep-fry by fully immersing in oil, the flavor improves.