alt Hacker News`out` params in C# are params that must be set within the function. They are way to implement multiple return values and tell the caller "this is written to, not read from."
But you might be conflating that with in/out for Contra/Co-variance when specifying a generic.
> They are way to implement multiple return values
They are one way to implement multiple return values. For multiple returns, tuples can be used. In fact, async methods can’t declare out params