I'm sure there are other definitions, but I use something like free will is about "the ability to make voluntary actions in line with your desires free from external coercion/influence".

Free will is key in morality and justice, so I like to understand how the courts define and use it. Lets use a real life example of how the Supreme Court considers free will.

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>It is a principle of fundamental justice that only voluntary conduct – behaviour that is the product of a free will and controlled body, unhindered by external constraints – should attract the penalty and stigma of criminal liability.
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>https://scc-csc.lexum.com/scc-csc/scc-csc/en/item/1861/index.do

In the case of R. v. Ruzic

>The accused had been coerced by an individual in Colombia to smuggle cocaine into the United States. He was told that if he did not comply, his wife and child in Colombia would be harmed.

The Supreme Court found that he didn't smuggle the cocaine of his own free will. He didn't do it in line with his desires free from external coercion. Hence he was found innocent.

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Compare that to the average case of smuggling where someone wants to make some money and isn't coerced into doing it. If they smuggle drugs then they did it of their own "free will" and would likely be found guilty.

You can also see how the courts aren't using the libertarian definition in Powell v Texas, where they tried a defence that it wasn't of their own free will since they were an alcoholic. While this argument shows they didn't have libertarian freewill, they did have compatibilist free will, hence they were found guilty.

So even if you are a hard determinist, you would need to use this idea around coercion(that the courts call free will). Even if you don't use free will by name you would have to use the concept.