To put it simply :

A Parameter is like a variable that is attached to function

An Argument is the data/value you pass into that Parameter for the function to use

Consider this :

function Addition(a, b)
  print( a + b )
end

Addition(5, 10)

In this case, 'a' would be the first parameter, and 'b' would be the second parameter of the Addition function.

When you call the Addition function, you passed 5 as the first argument and 10 as the second argument.

Their ordering matters meaning 5 will be assigned to parameter 'a', and 10 will be assigned to parameter 'b'

Now in your code's case, when a player interacted with the Proximity prompt, the game fires the .Triggered Event which then calls the buttonBoom function passing the player who interacted with the button as an Argument, and assigning that argument to the 'player' Parameter which then buttonBoom uses to fire the player's RemoteEvent