Sorry my bad - I know this wasnt you but someone was claiming that catholicism was a cult based on the Oxford English Dictionary so yeah my bad. this definition is also similar to the definition in the Macquarie Dictionary (2005) the International Standard Dictionary of the English Language (2000) and Collins Cobuild English Learners Dictionary (1994) which also implies that the marriage should be between a man and a woman.
Using the Marriage Act for definitional purposes only:
"marriage" means the union of a man and a woman to the exclusion of all others, voluntarily entered into for life.
MARRIAGE ACT 1961 http://www.austlii.edu.au/au/legis/cth/consol_act/ma196185/s5.html
Sorry I phrased that wrongly. What I meant to say is that by definition its suppose to be for a man and a woman. I wouldnt consider it as discrimination. Using the Discrimination Act for definitional purposes only the the general idea is that it is not considered discrimination if the grounds of the discrimination directly impact the nature of the activity e.g. it is not considered discrimination if a person does who cannot walk be denied a job which requires carrying heavy objects from one place to another just like it is not considered discrimination if universities deny access to those who have mental retardation (NSW Anti Discrimination Act 1977). Based on similar principles, same sex marriage would directly affect the nature of the activity because it is defined for the exclusiveness of man and woman and hence it should not be considered as discrimination.