星期二 (xīng qī èr) means “Tuesday”

More examples

我在星期二下午有空。wǒ zài xīng qī èr xià wǔ yǒu kòng

I am free on Tuesday afternoon.

The second place in the repeating seven-day calendar, after Monday and before Wednesday.

周二zhōu èr: A shortened spoken name for Tuesday, common in everyday schedules.
礼拜二lǐ bài èr: An everyday conversational name for Tuesday.

以一周七天为周期计算的第二天，通常为平日，用于说明日期和安排。yǐ yì zhōu qī tiān wèi zhōu qī jì suàn de dì èr tiān tōng cháng wèi píng rì yòng yú shuō míng rì qī hé ān pái

星期二 (xīngqīèr, "Tuesday") combines 星 (xīng, "star") + 期 (qī, "period") to form the word for a week and 二 (èr, "two") to identify its numbered day.

周二 (zhōu'èr, "Tuesday") is a shorter form often seen in calendars and schedules, so recognizing it helps when reading everyday plans.