Linux.conf.au (LCA) is a conference about Open Source Software, including Linux. It brings together the world's community of Linux and open source enthusiasts who make considerable contributions to open source software. It is not limited to just Linux users - the community is much larger than this.
The Open Source and Linux community are but part of a larger community with similar ideals. The Open Day is a chance for all these groups to make their presence known to the community at large.