To withdraw from something one has agreed to do.(verb)
To undo a change.(verb)
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Use "back out" in a sentence
"The deputies went back out the door, which was still open as Barry and Mr. Hindley worked."
"Ms. Ling slipped her arm around Taylors shoulders and helped her back out into the hallway."
"Upon hearing this good newsto which the word good was hardly sufficientI stripped down to my Sorel snow boots, stepped back out into the 5-degree air, and jogged around the house, barking my shins badly on a pile of lumber buried in the snow."