noun
left on; left running; constantly out; always appearing
Describes something that remains in a state of being out, on, or away without stopping. Often used for water left running, lights left on, or a person who is always out of the house or constantly in the public eye.
水道を出っ放しにしてしまった。
I accidentally left the water running.
彼は一日中出っ放しで、家にいない。
He's out all day and never at home.
出しっ放し is the transitive counterpart, meaning leaving something out or on (e.g., leaving a book out). 出っ放し is intransitive, describing the state of being out or on.
From 出る (deru, 'to go out') + っ放し (ppanashi, 'leaving something in a state'). The っ放し suffix indicates a continuous state, often with a nuance of neglect.