this

Từ điển American Heritage Dictionary 4th

this (thĭs)pron. pl. these (thēz)
1.
a. Used to refer to the person or thing present, nearby, or just mentioned:
This is my cat. These are my tools.
b. Used to refer to what is about to be said:
Now don't laugh when you hear this.
c. Used to refer to the present event, action, or time:
said he'd be back before this.
2. Used to indicate the nearer or the more immediate one:
This is mine and that is yours.adj. pl. these
1. Being just mentioned or present in space, time, or thought:
She left early this morning.
2. Being nearer or more immediate:
this side and that side.
3. Being about to be stated or described:
Just wait till you hear this story.
4. Informal. Used as an emphatic substitute for the indefinite article:
looking for this book of recipes.adv.
To this extent; so:
never stayed out this late. [Middle English, from Old English. See to- in Indo-European Roots.] 
Usage Note: This and that are both used as demonstrative pronouns to refer to a thought expressed earlier: The letter was unopened; that (or this) in itself casts doubt on the inspector's theory. That is sometimes viewed as the better choice in referring to what has gone before (as in the preceding example). When the referent is yet to be mentioned, only this is used: This (not that) is what bothers me: we have no time to consider late applications.·This is often used in speech and informal writing as an emphatic substitute for the indefinite article to refer to a specific thing or person: You should talk to this friend of mine at the Department of Motor Vehicles. I have this terrible feeling that I forgot to turn off the gas. It is best to avoid this substitution in formal writing except when a conversational tone is desired. See Usage Note at that.