That is one of the most common words in English and is used in a variety of ways. For example the phrases
She's the girl that I met last week.
OR
She's the girl I met last week.
are both correct! Learn when to use that, as well as when to drop that in this guide to the use of that.
One of the most common uses of that is in relative clauses. If you're not sure what a relative clause is, brush up your understanding with this relative clause explanation and follow-up relative clause quiz.
Comments
I learned that THAT is used for things and WHO is used for people. I’m no expert, but that’s what I have read.
She’s the girl WHO I met last week.
She’s the girl that I met last week.
She’s the girl I met last week.
Personally, I prefer the last example. It’s easier to omit a word if it really isn’t necessary.
Thanks for your useful ESL site, by the way. I often come here and appreciate help with English.