"She's off her L's and on her P's"
This is something you'll hear Australians say a lot particularly about teenagers.
What do you think this means?
A clue: it's to do with a rite of passage...
Well, would you believe this means that this person has successfully passed her practical driving test and now has a probationary driver's licence.
Australians ages 16-18 can do the theory test to get a learner driver's licence. Once they pass that, they then become 'L-platers', a term that comes from the yellow plate with a black 'L' (for 'learner') that all learner drivers must display on their car while driving. Hence someone who is a 'L-plater' is 'on their L's'.
Once they've passed the practical driving test and/or completed the log book, then they become 'P-platers', i.e. 'probationary drivers', who must display on their car a white plate with a red or green 'P' or a green or red plate with a white 'P' (depending on where in Australia). Therefore, they're 'on their P's'.

This being Australia, every state and territory has its own detailed regulations for obtaining a driver's licence, which go down to specific speed limits, the times when they are allowed to drive, the amount of passengers they may have in a car and for how long they are on their P's until they go on to their full licence.
It's not just teenagers who can be P-platers. Anyone who has had their driver's licence taken away for any reason go back to being P-platers for a certain period of time after regaining their licence.
Obtaining a driver's licence is very much a necessity for the sprawling, car-dependent nature of Australia's cities and towns where an overwhelming majority of Australians live. It's such a given that almost all Aussies have a driver's licence that the licence card itself serves the role of a de facto national ID card in Australia.
For many Aussies, the concept of an adult not having a driver's licence is simply unfathomable. For you adult non-drivers, I dare you to say to an Aussie that you don't have a driver's licence. The reaction will be priceless 😁

And note...
🪪 in Australia 🇦🇺 and Canada 🇨🇦 it's a 'driver's licence'
🪪 in the UK 🇬🇧, Ireland 🇮🇪, South Africa 🇿🇦 and India 🇮🇳 it's a 'driving licence'
🪪 in the US 🇺🇸 it's a 'driver's license'
🪪 in New Zealand 🇳🇿 it's a 'driver licence'
Goes to show that it's the little differences between the variants of English that matter.
Need help in knowing your L's from your P's when dealing with the Australian market? Trust your text and copy to someone with many years' experience... me! Email me at info@nicknasev.com and let's discuss.