You buy one option only, you own one option only. Its not a...

You buy one option only, you own one option only. Its not a share nor do you own one...

Unless you convert. Convert one option only paying the excise price. Then you own a share.

If you do not convert by the excise date, you loose all your options.

Thats for trading what im assuming you're talking about with RMR options which are coded "RMRO"

Then there are other types of options trading which is explained here: http://www.asx.com.au/documents/resources/UnderstandingOptions.pdf