Can I install pantheon terminal in Ubuntu 14.04 or newer?

You can install it by running:

sudo add-apt-repository ppa:elementary-os/stable
sudo apt-get update
sudo apt-get install pantheon-terminal

The ppa:elementary/stable is recommended for LTS releases of Ubuntu.

The ppa:elementary/daily may be used for any currently supported releases of Ubuntu and has the newest and most unstable development of elementary. The Daily PPA is subject to critical bugs and should not be used except for testing purpose only.

Do note that, since Pantheon often uses a different version of GTK than Ubuntu (especially with LTS), this may impact your system with broader impact (IE: Gnome issues), so thar be dragons

Pantheon terminal requires gtk >= 3.12, but Ubuntu 14.04 comes with gtk 3.10

So at the moment it is not installable unless you want to add gnome3 staging ppa, which is not recommended and will probably break your system.