Essentially, it means that you really dig it here on Earth, and that you are compelled to absorb and savor every ounce of every experience that constitutes your existence. Eventually, when you die, hopefully at a very ripe old age, you will be content with the knowledge that you gave it your best shot, you never let your enthusiasm wane, and you never lost your grip on reality.
If you have a lust for life then you try to enjoy every moment and take up every opportunity to do new things, meet new friends, and go different places.
Lust for life is a tremendous love of life. Enjoying every moment . Wanting to live life to its fullest
It means that you want to expose all of life's pleasures to the fullest. You want to taste all her fruits, bitter and sweet. It means each night you long for the next day. It means too much is never enough, and sleep is inessential, non substantial. It is then that you lust for life.