Gerunds are the nominal forms (noun forms) of verbs, that is, verb forms in
-ing used as nouns.
Present (and past) participles are adjectival forms of verbs. The present participles are verb forms in
-ing used as adjectives.
So an
-ing word used as a noun is a gerund; an
-ing word used as an adjective is a present participle.
a long stick - a walking stick Both "long" and "walking"
are adjectives. In this context "walking" is a present participle.
colorful parrots - speaking parrots. Both "colorful" and
"speaking" are adjectives. In this context "speaking" is a
present participle.
an efficient machine - a washing machine Both "efficient" and
"washing" are adjectives. "washing" is a present participle.
a machine for the purification of chemicals - a machine for
washing Both "purification" and "washing" are nouns.
"washing" is a gerund in this context.
a machine that purifies - a machine that washes. Both "purifies"
and "washes" are verbs. There are no gerunds or participles here.
fires are prohibited in this area - hunting is prohibited in this
area. Both "fires" and "hunting" are nouns. "hunting" is a
gerund in this context.
One note of caution:
-ing words that denote physical objects are plain nouns, not gerunds.
The building collapsed. "building" is a noun, but not a gerund.
CJ