I'm studying through man gitglossary, and this one term has eluded me—because it isn't defined in the glossary at all.
It's referred to only twice (asterisks added):
alternate object database
Via the **alternates mechanism**, a repository can inherit part of its
object database from another object database, which is called
"alternate".
repository
A collection of refs together with an object database containing
all objects which are reachable from the refs, possibly accompanied
by meta data from one or more porcelains. A repository can share an
object database with other repositories via **alternates mechanism**.
What is the "alternates mechanism" that is referred to here?