What is being done there is a pro-form substitution (replacement); "this/that" are called
I think that in this case "a pronoun substitutes a noun or a noun phrase, with or without a determiner" such as it or this.
Add-on: By the way, seeing that others include the explanation of deictics, I thought I'd include it too.
I didn't mention it because it didn't seem fundamental to answer your question, but it can add value to the discussion. Like others said, we have deictics in languages. They are highly dependent to the context, and if you listen to an audio conversation, they might represent a problem if you want to fully understand that dialogue. I had some notes about this matter: "Deictic" comes from the Greek word for "pointing" or "indicating". It is reference by means of an expression whose interpretation is relative to the context of the utterance, such as:
a) who is speaking
b) the time or place of speaking
c) the gestures of the speaker
d) the current location in the discourse
e) the topic of the discourse
If near speaker, proximal terms are used (this, here, now); if away from speaker, distal terms are adopted (that, there, then). Speakers and hearers constantly adjust their internal registry of deictics to keep up with the conversation.
Traditionally, by deixis is meant the location and identification of person, objects, events, processes and activities being talked about, or referred to, in relation to the spatiotemporal context created and sustained by the act of utterance and the participation in it, typically, of a single speaker and at least one addressee; we can analyze them this way:
- Person deixis: those that are used to refer to speaker and addressee (I, you, we)
- Place deixis: those that refer to spatial context (here, there)
- Time deixis: these that refer to temporal context (now, then, verb tense markers)
- Discourse deixis: those that refer to parts of unfolding discourse (next, below, furthermore)
- Social deixis: those that encode aspects of the social relationship between speaker and addressee (Her Majesty)
- Perceptual deixis: There's Harry