Deixis is also mentioned as indexicals. By deixis, we mean pointers or something that points to other things. In order words, indexicals are linguistic forms or expressions that refer to other things. In a sense, deixis can be a synonym of language expressions. For that reason, deixis is one of the essential and earliest marking elements of pragmatics, and falls under pragmatic investigation at the very birth of this independent field of learning.

Deixis refers to the world outside a text. Reference to the context surrounding an utterance is often referred to as primary deixis, exophoric deixis or simply deixis alone. Primary deixis is used to point to a situation outside a text (situational deixis) or to the speaker's and hearer's (shared) knowledge of the world (knowledge deixis).

There have been lots of documentations about deixis. The most influential study can be credited to Charles Fillmore’s Santa Crusez Lectures on Deixis in 1971.
According to Fillmore, deixis can be roughly categorized into five types. They are deixis of person (pronominal deixis), deixis of place (spatial deixis), deixis of time (temporal deixis), deixis of discourse (discoursal deixis), and deixis for social purposes (social deixis).

Pronominal deixis refers to a person pointer or assigner. “He”, “I”, etc are typical examples.
Spatial deixis denotes a place pointer. Examples include “here”, “there”, “this”, “that”, “up”, “down”, “north”, “inside”, “top”, “bottom”, etc..

There are many temporal deixis in our language. “Now”, “then”, “from now on”, “last year”, “in the future”, etc. are all examples of this kind.

A discoursal deixis is self-explicit in that it is used primarily in a discourse unit and for discoursal purposes. We employ discoursal deixis a lot for textual coherence or as procedural indicators. For instance, we use “to begin with”, “first”, “next”, “in the following paragraph”, “last but not the least”, etc. to smooth the transitions or connections between different parts of a textual unit.

Apparently a social deixis is for the sake of politeness in social interaction.