pen vs holding yard

pen and holding yard both are nouns.

Word	Noun	Adjective	Verb	Adverb
pen	Yes	No	Yes	No
holding yard	Yes	No	No	No

As nouns, holding yard is a hyponym of pen; that is, holding yard is a word with a more specific, narrower meaning than pen:

pen (noun)	holding yard (noun)
female swan	a pen where livestock is temporarily confined
a writing implement with a point from which ink flows
an enclosure for confining livestock
a correctional institution for those convicted of major crimes
a portable enclosure in which babies may be left to play

pen (verb)	holding yard (verb)
produce a literary work