This is GIT's file system checker, which makes sure that every available object is reachable and valid.
When references like branches are deleted, the objects (e.g., Commit objects) aren't usually deleted but aren't reachable.
This is useful (as with reflog) to recover deleted branches, but especially useful with recovering remote branches.
git branch bug-fix master * new-feature git checkout master Switched to branch 'master' git branch bug-fix * master new-feature git rev-parse --short new-feature c033e5e git branch -D new-feature Deleted branch new-feature (was c033353). git fsck --lost-found Checking object directories: 100% (256/256), done. dangling commit 4113bc5d0d3ad3047e76b0ea67e8d8bc82f74821 dangling commit c033e5e21e2a89920a1a8b0a4e31d16b423e420b dangling blob c700db9f3785252428d20bb87f09a33d634dd9f1 dangling tree 4b825dc642cb6eb9a060e54bf8d69288fbee4904 dangling commit ff70d170cb69f044fb595d06ce90a3c6962bfe82 git branch bug-fix * master git branch new-feature c033 git branch bug-fix * master new-feature