This is a blessing, usually used to wish the elderly good health and a long life. This greeting can be used in many occasions, such as the birthday of the elderly, major festivals, illness and so on.
Of course, besides this greeting, we can also use other expressions to wish the elderly a long and healthy life, such as "five blessings", "Happiness as the East China Sea, Longevity as the South Mountain", "Good health, long life" and so on.