Verbal Noun

A verbal noun is a noun formed from or otherwise corresponding to a verb. Different languages have different types of verbal noun and different ways of forming and using them. An example of a verbal noun in English is the word singing in the sentence "Singing is fun" (this is a noun formed from the verb sing).

Using a verb as a noun

The verbal noun just refers to any noun that has been derived from a verb. For example, the word "flight" is a verbal noun, because it is derived from the noun "fly". 

A gerund is a special form of verbal noun: this is when the suffix -ing is added to the root form of a verb in order to turn that verb into a noun referring to an activity (like "reading"). 

Creating verbal nouns in a sentence

Here is an example of the verbal noun being used correctly within a sentence. 

"Thanks to the late arrival of his plane, the man had to skip dinner if he was to meet up with his friends at the planned time." 

In this sentence, the word arrival is a correctly used verbal noun. 

Now, here is an example of the incorrect use of the verbal noun. 

"The man was watching television when he suddenly realized that he was going to be late for his job interview." 

In this sentence, watching television is not a verbal noun, because it is being used as a progressive verb phrase and not as a gerund. 

For your reference, here are a couple rules you can follow in order to make sure that you are using the verbal noun in an appropriate way.

1. Often, you may use verbal nouns without even realizing you're doing it. This is because in English, it is quite common for a noun to be formed out of a related verb. This is just in the nature of language development, and it probably isn't something you need to consciously think about in everyday language use. 
2. Regarding the specific verbal noun form known as the gerund, you need to ask yourself: what role is this phrase playing within the sentence? The gerund and the progressive verb conjugation can look exactly the same, so you'll need to think about the function played by the phrase in order to tell the difference. 

Verbal nouns primarily used in linguistics

The actual concept of the verbal noun may primarily be of use only to linguists. This is because as far as everyday language use is concerned, people likely use verbal nouns all the time without even being conscious of this fact—and moreover, they are likely using it in a correct way. This is especially the case for a common verbal noun, like departure and arrival, that is related to verbs but always used in an independent way.   

Aside from words actually formed from verbs, the verbal noun can also refer to when a verb becomes a noun within the context of a given sentence. The gerund is a good example of this; and the infinitive also sometimes fulfills this kind of function. Here, the correct use of the verbal noun can become a little more complicated, insofar as phrases that are commonly thought of as verbs are now fulfilling the function of a noun. Even here, though, regular practice of a language usually enables speakers to find the right uses in a natural and more or less unreflective way.