Nudism & flasher
The difference is the intention.
I flasher deliberately exposes their naked body to other people whether they want to see it or not, for sexual pleasure.
A naturist gets naked for pleasure too, but that pleasure is directly as a result of being naked, such as comfort, freedom, the feeling of the sun and the breeze on your skin. All real benefits and an enjoyment to the nudist alone.
There is another "category" if you like, the exhibitionist, who likes being seen and seeks situations where they will be seen. While there may also be some sexual gratification in this too, that's not necessarily so. It could just be the excitement of pushing the "social envelope".
If you are doing everything reasonably possible to provide privacy in your garden then you are definitely not a flasher or exhibitionist. If your neighbour done see you, and complains to you or the police, you will have the defence that you have already done all you reasonably can to prevent it.
There is a legal difference here in the UK. Naturists are treated as a minority group with rights of self expression. It is not illegal for a naturist to go about his lawful business, even in public, without clothes. There is a proviso: the naturist must not intentionally cause Alarm or Distress to those around him. The actions of a flasher are deemed to intentionally cause Alarm an Distress as it is done to shock the viewer. So it is illegal.
Many of our laws in Australia follow from the UK, I'm not sure about naturists being considered a minority and having rights of self expression or freedom of expression but I'll have to do some research. I'd like to think that the law would interpret that you are not a flasher if you are enjoying your own yard and that you are not trying to be seen or cause an issue.
I think its an example of where the UK and Australian laws have diverged over time. I've never had concerns with skimpy bathing suits (including a thong if a very quiet day), but nude is different in Australia. It would be defined in state legislation.