THING › used to refer to the thing, situation, or idea that has already been talked about: "Have you seen my bag?" "It's in the hall." It was a horrible argument and I don't want to talk about it.
DESCRIPTION › used before certain adjectives, nouns, or verbs to introduce an opinion or description of a situation: It's unlikely that she'll arrive on time. It's a pity you can't come with us.
SUBJECT/OBJECT › used with certain verbs that need a subject or object but do not refer to a particular noun: It costs less if you travel at the weekend. I liked it in Scotland.
TIME/WEATHER › used with the verb 'be' in sentences giving the time, date, weather, or distances: It rained all day. What time is it?
SEEM › used as the subject of verbs such as 'seem', 'appear' and 'look': It seemed unfair to leave her at home.
EMPHASIZE › used to emphasize one part of a sentence: It's the children I'm concerned about, not me.
it's sb/sth › used to say the name of a person or thing when the person you are speaking to does not know: It's your Dad on the phone.