It's a traditional Jewish greeting used during Rosh Hashanah, the Jewish New Year, to wish someone a happy and prosperous year.
Here's a breakdown of the phrase:
* Leshana tova: "A good year"
* Tekatev: This part is an abbreviation for "tekatvu ve'hitkatvu" (תִּכָּתְבוּ וְהִתְכַּתְּבוּ), which means "may you be inscribed and sealed [in the Book of Life] for a good year."
So, the entire phrase expresses a heartfelt wish for a good year filled with blessings and good health.