Deixis is the phenomenon that elements in a language may have a reference which is dependent on the immediate context of their utterance. The term is introduced to handle the 'orientational' features of language which are relative to the time and place of utterance.
(i) personal pronouns: I, you, he, etc.
(ii) adverbials of place and time: here, there; now, then
Deixis is merely the Greek word for 'pointing' or 'indicating'.
Lyons, John. 1968. Introduction to Theoretical Linguistics. Cambridge: Cambridge University Press.