terminal: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On CentOS possible default full paths are:

/usr/bin/terminal - from package: Terminal

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/terminal - from package: terminal.app

You may install the required package with command apt-get install {package}

Error in other languages:
terminal: bevel nie gevind nie
terminal: comandă negăsită
terminal: comando não encontrado
terminal: commande introuvable
terminal: command not found
terminal: käsku ei ole
terminal: không tìm thấy lệnh
terminal: komanda nerasta
terminal: Kommando nicht gefunden.
terminal: kommandot finns inte
terminal: komut yok
terminal: nie znaleziono polecenia
terminal: níor aimsíodh an t-ordú
terminal: no se encontró la orden
terminal: no s'ha trobat l'ordre
terminal: opdracht niet gevonden
terminal: parancs nem található
terminal: perintah tidak ditemukan
terminal: príkaz nenájdený
terminal: příkaz nenalezen
terminal: команда не найдена
terminal: командата не е открита
terminal: 命令找不到
terminal: コマンドが見つかりません