The binary is called apt-get. There are others like apt-cache etc.

Apt is a script that just figures out which binary to use and passes the arguments on.

• apt update -> apt-get update
• apt policy -> apt-cache policy

These days, apt is for humans whereas apt-get is for scripts. apt’s output is designed for humans and may change between releases, whereas apt-get is guaranteed to remain consistent to avoid breaking scripts.

apt combines several commands together. For example, you can use it to install packages from both repos and local files (e.g. apt install ./foo.deb) whereas apt-get is only for packages from repos and you’d need to use dpkg for local packages.