The conditions on a Visitor ETA are:

• It is valid for visits to Australia for tourism or to visit friends or relatives
• It is valid for multiple visits within 12 months from date of issue
• The maximum length of each visit is three months
• You may not work while in Australia

The conditions on a Short Validity Business ETA are:

• The Short Stay Validity Business ETA is appropriate for visits to Australia for business meetings, conventions, conferences or a short term project requiring a high level of skill. Business visas are subject to a condition prohibiting work that could otherwise be undertaken by any Australian citizen or permanent resident. Generally, persons seeking to engage in paid employment in Australia should apply for the Temporary Business Entry (Long Stay) visa - subclass 457 or other appropriate class of visa.
• It is valid for a single visit within 12 months from date of issue
• The maximum length of the visit is three months

For both types of ETA, remember that you will not be permitted to enter Australia unless you are in good health and have no criminal convictions.