Gpg agent

gpg-agent is a daemon that caches secrets in memory.
secrets can be retrieved/stored from processes by communicating with gpg-agent over a socket.
gpg itself interacts with gpg-agent, either requesting/reusing or retreiving/caching a secret.

One use of gpg-agent is to cache your password-protected keys with a configurable timeout.

Documentation

man gpg-agent

https://man.archlinux.org/man/core/gnupg/gpg-agent.1.en

Tutorials

SO: how gpg-agent works

https://unix.stackexchange.com/questions/188668/how-does-gpg-agent-work