Ud meah vesrim means until 120 (bis hundertzwanzig in Yiddish). You say it on someones birthday, 21 today, ud meah vesrim.
It is a blessing you utter when talking about someone who is very old, My great grandmother, ud meah vesrim. It is also used when talking about someone in bad health, Poor fellows had his second bypass operation, ud meah vesrim, or in a conversation where there might be the slightest doubt in your listeners mind about whether you actually want the person being spoken about to survive until age 120, My spinster aunt, ud meah vesrim, is actually worth several million.
The blessing comes from the lifespan of Moses; Moses was 120 years old when he died (Deuteronomy 34:7). I have often wondered why we do not say until 147 (like Jacob) or until 175, the years of Abraham, or even until 969, the lifespan of Methusaleh. Apart from fact that these are not realistic expectations today, whereas 120 is (very nearly), it may be because the Torah tells us that Moses lived in perfect health and vigour until his last day; his eyes were undimmed, and his life-sap unabated (Deuteronomy 34:7.). We are not just wishing someone a long life, but a healthy and energetic one to the end.