I happened upon a page of the Purdue Online Writing Lab about gerunds. I note that this service from Purdue University is not a "lab" about "online writing" but an "online lab" about "writing". You probably knew that, didn't you? That's because you are fluent in English. If you are fluent in English, you'd know that "online writing" is not a typically used category, whereas a university website might very likely have an "online lab". Based on this probability analysis you, the English speaker, make the reasonable judgement that the title refers to a World Wide Web enabled workspace which deals with the subject of writing.
Simple.
Let us turn then to the topic of this particular page within the Purdue Online Writing Lab: Gerunds. According to this page, "A gerund is a verbal that ends in -ing and functions as a noun." They give this example:
My cat's favorite activity is sleeping. (The gerund is sleeping.)
Let us be clear. Sleep is a verb; sleeping is a form of the verb. Of course, sleep is also a noun (what I didn't get enough of last night) and an adjective ("sleep apnea", as opposed to wakeful apnea). Among other things. Because this is English. And English Is Weird.
So, a gerund (in English) is a form of a verb which is used as a noun. Now, any form of any verb can be used as a noun, so this is no big thing. For example, paint is a verb that can be used as a noun. (Or is it a noun that can be used as a verb?) I can paint the house with paint. Similarly, I can house the plants in the house, or I can plant the plants in the garden, a place where I will garden all summer. But those aren't gerunds. No. A gerund can only be the form of the verb ending in -ing. Like "ending". Except that one was a participle.
It isn't entirely clear why words that are based on verbs and end in -ing are given a special name by the linguists and school teachers. I sometimes suspect that they just needed a title for the next section. Perhaps they borrowed "gerund" from descriptions of some other language, probably Latin, in order to seem more refined and educated. Because in English these are all just words.
In fact, the very same word can be assigned all sorts of names. For example, crying will be called a gerund when you say that crying is good for the soul (assuming that you ever say that) but it will be called a participle when you are listening to a crying baby because a participle is a form of a verb used as an adjective. (Of course, any form of a verb can be used as an adjective, such as a light walk, or a walk light, or a walking stick, or a stuck record.)
The example was:
My cat's favorite activity is sleeping. (The gerund is sleeping.)
Actually, my cat's favorite activity is stalking small animals, but sleeping does rank high. Many times my favorite cat is sleeping. Those small animals he watches are also sometimes sleeping. But favored or disfavored, no activity is ever found sleeping. You have to be a multicelled living being in order to sleep. So why would we say that any "activity is sleeping"?
They say -- the linguists and the teachers I mentioned above -- that sleeping is a gerund when it is used as a noun. It would be a participle when it is used as an adjective. Or is it that sleeping is a gerund when it is understood as a noun?
I think that English words are all just words and nothing more. All the words in a sentence modify each other. Together they evoke an idea. If the words are well chosen and well arranged then the idea they evoke in your mind as the reader will mirror the idea I had in my mind as the author. When that happens, we communicate. I'm not sure that I ever use words as nouns and verbs, let alone as gerunds.
English Is Weird, but not quite so weird as the insistence that English usage can be analyzed and categorized according to fixed principles.
When I say "running" the word no doubt raises a plethora of associations: sights, sounds, rhythms, memories; athletes, brooks, engines, politics. When I say "shoes" other associations are raised. "Running shoes" filter these associations to an intersection of ideas, most likely a subset of kinds of shoes, but perhaps an image of shoes escaping from the slavery of the clothes closet in order to explore the world and to live as Free Footware. Couldn't "eye glasses" be containers for excised organs of sight? The point is that in the English language, perhaps even more than in others, communication depends on the active involvement of both parties: the writer and the reader, the speaker and the hearer.
English does not brook arbitrary categorization of its forms and parts. The beauty of the English language is its glorious ambiguity. Which may be why the Purdue Online Writing Lab also gives this example:
Finding a needle in a haystack would be easier than what we're trying to do.