Halliday & Matthiessen (2014: 609n):
Cohesive conjunctions have also been called ‘discourse markers’, but many other terms have been used as well (e.g. ‘discourse particle’, ‘connective’; and in computational linguistics/natural language processing: ‘clue word’, ‘cue phrase’) and the term ‘discourse marker’ has also been used to include items other than cohesive conjunctions, e.g. textual continuatives but also interpersonal items (see, e.g., Schiffrin, 1987, 2001; Fraser, 2006, and other contributions to Fischer, 2006). Fraser (2006) uses the term ‘discourse marker’ in the sense of ‘conjunction’, treating it as a type of ‘pragmatic marker’; Schiffrin (1987) uses the term ‘discourse marker’ in a broader sense. Aijmer & Simon-Vandenbergen (2009) present different senses of the term ‘pragmatic marker’, and make the point that in systemic functional linguistics such markers are either interpersonal or textual.