What is this "Part" Parameter in the script?

Hi, I am making a group rank door. Only certain ranks or above can go through. But if not the right rank, I want the person to be killed to be set back to spawn. I have it working, but I need helping understanding certain parts.

function onTouched(part) -- part? What is that? I know it is a Parameter. What does it do?
	if game.Players.LocalPlayer:GetRankInGroup(2934469) >= 10 then
		script.Parent.CanCollide = false
	elseif part.Parent:FindFirstChild("Humanoid") ~= nil then -- part here? What does it do?
	part.Parent.Torso:BreakJoints() -- part here? What does it do?
end
end


script.Parent.Touched:connect(onTouched)

Thanks, Vincent Lauro

function onTouched(part) -- part is the part that the script's parent touched
    if game.Players.LocalPlayer:GetRankInGroup(2934469) >= 10 then
        script.Parent.CanCollide = false
    elseif part.Parent:FindFirstChild("Humanoid") ~= nil then -- This looks to see if the part's parent contains a Humanoid
    part.Parent.Torso:BreakJoints() -- This kills the player if they don't have a high enough rank. It breaks the joints of the character's Torso
end
end


script.Parent.Touched:connect(onTouched)