っぱなし is a 接尾語（せつびご） (suffix) that originally comes from the う - Verb 放（はな）す ‘to let loose’. When attached to the 連用形（れんようけい） (conjunctive form) of verbs, it is used to indicate that something has been ‘left’ in a certain state.
っぱなし is almost exclusively used negatively.
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また電気（でんき）点（つ）けっぱなしじゃん！何回（なんかい）言（い）えば消（け）してくれるの？
You left the light on again! How many times do I have to tell you to turn it off?
冷蔵庫（れいぞうこ）を開（あ）けっ放（ぱな）しにしないで下（くだ）さい。
Please don't leave the refrigerator open.
歯（は）を磨（みが）いている間（あいだ）、水（みず）を出（だ）しっぱなしにしていたら、お母（かあ）さんに怒（おこ）られた。
Because I left the water on while I was brushing my teeth, my mother scolded me.
Although 放（はな）す means ‘to let loose’,
っぱなし conveys a feeling that is closer to ‘being unchecked’. This means
っぱなし can be used to convey that ‘the act of (A)’ is continuing without anyone there to stop it, or that the ‘state of (A)’ is continuing without anyone there to stop it. Which meaning is conveyed will depend mostly on the (A) verb.
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勝（か）ちっぱなしだとつまらないね、たまには負（ま）けを味（あじ）わいたい。
Don't you think it is boring to keep winning? I want to taste defeat sometimes. (I want to lose sometimes)
秋（あき）の間（あいだ）は窓（まど）を開（あ）けっぱなしにして寝（ね）ています。
During autumn, I sleep with the windows left open.