railing vs barrier

railing and barrier both are nouns.

Word	Noun	Adjective	Verb	Adverb
railing	Yes	No	No	No
barrier	Yes	No	No	No

As nouns, barrier is a hypernym of railing; that is, barrier is a word with a broader meaning than railing:

railing (noun)	barrier (noun)
a barrier consisting of a horizontal bar and supports	a structure or object that impedes free movement
material for making rails or rails collectively	any condition that makes it difficult to make progress or to achieve an objective
	anything serving to maintain separation by obstructing vision or access