I always understood you were classified by the ATO as a business or 'enterprise' if it was with the intention of making a profit?

From ATO site:
Am I in business?

Why does it matter whether my activity constitutes a business?
It matters because it affects whether:

-any money you receive from the activity is assessable income
-any loss you make can be offset against other income you earn in that year or in future years
-you need an Australian business number (ABN), and
-you can register for goods and services tax (GST).

If you are carrying on a business then you are entitled to an ABN. You may choose to register for GST if your annual turnover is less than $50,000. However, you must be registered for GST if your annual turnover is $50,000 or more.

Additionally, any payments that are paid to you in relation to supplies that you make to another business may be subject to pay as you go (PAYG) withholding (at a rate of 46.5%), if:
you do not quote an ABN on an invoice or other document relating to the supply, and
certain exceptions do not apply.

For further information on when payments may be subjected to PAYG withholding when an ABN is not quoted, see Taxation Ruling TR2002/9 `Income tax: withholding from payments where recipient does not quote ABN'.

You are not entitled to an ABN if:

-your activity is a hobby or a private recreational pursuit, or
-you are an individual or a partnership mainly of individuals, and there is no reasonable expectation of profit or gain from the activity.
My bookkeeping business is definitely under $50k, but there's no way it's a hobby, as my plan was to make money from it!