There are many other useful expansions on the notion, but I like his for its clarity and common sense. If you remember just the sentences "A gerund is always a noun and verb at the same time. It is type of verbal noun, a noun that has verbal properties as well" and approach any use of the gerund that puzzles you in the light of that statement, the light bulb will go on.

There is never a use of the gerund in English when it does not have the properties of a noun. I can't improve on tchrist's answer, and his viewpoint aligns with mine. John Lawler, who knows a thing or two, says: "If it ends with -ing and it's got a direct object, it's a verb and therefore a gerund. If it ends with -ing and it takes an article, it's a noun and therefore not a gerund.."

So you see, the matter isn't settled, and it isn't very important, either. What is important is that you yourself define the English gerund in a way that allows you to use it and understand it without any conscious thought or effort, just as snailplane and I and tchrist and John Lawler do. Although I agree with his reasoning, I don't believe that tchrist's answer is "the correct answer" to the question "Is the gerund a noun or a verb?" nor that snailplane's is, nor Lawler's.

Of course, I still think I'm right about this!