Definition
Plain language
Sending your local code changes up to the shared copy everyone else can see.
As stated in the literature
Uploading local commits to a remote repository ref; in exfiltration scenarios it is the boundary-crossing step, since it moves content out of the local sandbox into a network-visible host.
Why it matters: Pushing is the moment local work becomes visible on the network, which makes it both the point of collaboration and a natural chokepoint for data leaving a sandbox.
For example, after finishing a fix on her laptop, a developer runs git push and her commits appear on the team's shared server where teammates can pull them.