The definition of 'object' is outside of the scope of the documentation for the 'push' command. Similarly with 'ref'. From "man git": "The object database con

The definition of 'object' is outside of the scope of the documentation for the 'push' command. Similarly with 'ref'. From "man git": "The object database contains objects of three main types: blobs, which hold file data; trees, which point to blobs and other trees to build up directory hierarchies; and commits, which each reference a single tree and some number of parent commits. The commit, equivalent to what other systems call a "changeset" or "version", represents a step in the project's history, and each parent represents an immediately preceding step. Commits with more than one parent represent merges of independent lines of development. All objects are named by the SHA-1 hash of their contents, normally written as a string of 40 hex digits. Such names are globally unique. The entire history leading up to a commit can be vouched for by signing just that commit. A fourth object type, the tag, is provided for this purpose. When first created, objects are stored in individual files, but for efficiency may later be compressed together into "pack files". Named pointers called refs mark interesting points in history. A ref may contain the SHA-1 name of an object or the name of another ref. Refs with names beginning ref/head/ contain the SHA-1 name of the most recent commit (or "head") of a branch under development. SHA-1 names of tags of interest are stored under ref/tags/. A special ref named HEAD contains the name of the currently checked-out branch."