/DIs/ determiner plural these
1 used to talk about a person, thing, idea etc that has already been mentioned or that the person you are talking to already knows about: Wait till you hear this joke. | What is the purpose of your visit to this country? | There will be another meeting later this week. | How can we help these poor children? | If we carry on at this rate we'll be bankrupt by the end of the week.2 used to talk about the person or thing nearest to you or the time that is soonest etc: I'm going to visit my Mum this Wednesday. | I'll look in these rooms if you look in all the rest. | I'm surprised you like that photo - I prefer this one.3 spoken used in stories, jokes etc when you mean a person or thing, especially when you do not know their name: When am I going to meet this boyfriend of yours? | I met this really weird guy tonight.4 this minute/second immediately: I want to see you in my office this minute!2 pronoun plural these1 used to talk about a person, thing, idea etc that has already been mentioned or that the person you are talking to knows about already: Where did you find these? | This is terrible. What on earth are we going to do? | If you think that's funny wait till you hear this.2 used to talk about the person or thing nearest to you, the time that is soonest etc: These are your coats, aren't they? | That might be a much prettier dress but I feel more comfortable in this.3a) informal used to introduce someone to someone else: Sam, this is my sister, Liz.b) used when you have answered the telephone and you want to give your name: “Can I speak to Joan please?” “This is Joan speaking.”4 a particular time: I thought he would have been back before this. | Well young lady, what time do you call this?5 this, that and the other also this and that especially spoken various different things, subjects etc: “What have you two been gossiping about all evening?” “Oh this, that and the other.”6 what's (all) this? spoken used to ask what is happening, what someone's problem is etc: What's this? Crying again?3 adverb (+ adj/adv) this big/many etc spoken used to say how big or how many, especially because you are showing the size, number etc with your hand: this big/tall etc: The table's about this high and this wide. | this much/many: Do you know he cut this much off my fringe without even asking me!
Longman dictionary of contemporary English. 2004.