Quick Question about Elseif?

First of all, elseif is not a function. It is a keyword.

The difference between elseif and else is that the former lets you specify a new condition which must be true for the block to be entered, while the latter executes if and only if all previous if and elseifs failed.

It is really just a combination of else and if:

if A then
	-- do something if `A` is true
elseif B then
	-- do something else if `A` is false but `B` is true
end

is equivalent to

if A then
	-- do something if `A` is true
else
	if B then
		-- do something else if `A` is false but `B` is true
	end
end

The former is clearer and should be preferred.