Depends on your definition.
In some countries, a "simple majority" is whoever gets the most votes. Then you have an "absolute majority" which is when you require more than 50% of votes.
https://peo.gov.au/understand-our-parliament/your-questions-on-notice/questions/in-parliament-which-votes-require-a-simple-majority-and-which-votes-require-an-absolute-majority/
A simple majority is still a majority, not a plurality. As your own link says:
Most ideas – motions – are agreed to by a simple majority. A simple majority is when a majority of those who are present agree to the idea.
This isn't just the "most votes" though I certainly do not know if either house of the AU Parliament can have motions with more than two options like in the case of this Speaker vote the wording seems to indicate that if this was possible a majority would still be needed.
From a corresponding question:
The Australian Government is part of the Australian Parliament. After a federal election, the party or coalition of parties with the support of the majority – more than half – of members elected to the House of Representatives becomes the government.
To remain in office the government must keep the support of the majority in the House of Representatives.
I can't seem to find out at the moment how Australia does it. Do they up/down vote a single PM candidate until someone gets approved or are all the parties leaders (plus randoms) nominated and there's a single ballot? Some countries (typically the French-Spain sphere) do one way and others (typically the UK sphere, which is why the US Speaker vote and the Electoral College is like this) do the other way.
Australian parties go to an election with a "nominated" leader.
If that person wins their seat at the election, the parliament meets and it is usually a formality for that person to be nominated by the house to sit as Prime Minister and to form government. As long as they have an absolute majority in the lower house (MPs rarely cross the floor and they would never cross the floor when deciding who will be PM). That nominated PM then goes to visit the Governor-General who will swear in them and their cabinet (must be MPs/Senators from the lower and upper house) in as a government.
If the party with the most lower house seats does not win an absolute majority (what we refer to as a simple majority), they must govern with the support of minor parties or independents (forming a minority government). They have the numbers only because there is an agreement with the independents to guarantee supply. This has happened quite often in federal and state parliaments. Until a new PM is sworn in, the old PM remains in a caretaker capacity.
If no party can get the support needed to guarantee supply, or they lose the support of the minor parties/independents during their term, then we go back to another election.*
*I am 99% sure this is how all this happens. It's been a while since I learned all this stuff.
