「お茶」 (ocha) means "tea," often specifically "green tea" in Japan. It's a popular beverage made by infusing tea leaves in hot water. You use 「お茶」 when offering or requesting tea. 「日本人はよくお茶を飲みます。」 (Japanese people often drink tea.)

日本で特に一般的な、茶葉を煮出した飲み物です。緑茶を指すことが多いです。