On Saturday evening or Sunday morning, someone may greet you with the phrase “Shavua tov!” (shah-VOO-ah TOHV).
It means “Good Week!” and it’s the greeting for the new week that begins at sundown on Saturday night. Remember, all Jewish days begin and end at sundown.
You’re most likely to hear it Saturday evening or Sunday morning, but it’s still appropriate (if a little belated) until sundown on Wednesday. You’ll rarely hear “Shabbat shalom” until Friday.
So if someone says “Shavua tov!” to you, you can say right back to them, “Shavua tov!” Alternatively you can say, “Gam l’cha!” if they are male and “Gam lech!” if they are female. Either way, it means “Also to you!” or “Backatcha!”