What's the difference between a gerund and a participle?

What is the difference between a gerund and a participle?

A gerund is a form of a verb used as a noun, whereas a participle is a form of verb used as an adjective or as a verb in conjunction with an auxiliary verb.

In English, the present participle has the same form as the gerund, and the difference is in how they are used. When used with an auxiliary verb ("is walking"), it serves as a verb and is the present participle. When used as an adjective ("a walking contradiction") it is also a participle. However, when used as a noun ("walking is good for you"), it is a gerund.

See the Wikipedia articles on gerund and participle for more details.

A gerund is used as a noun, a participle as an adjective.

Gerund:

Traveling is fun.

Participle:

The traveling man stopped.

The Purdue Online Writing Lab has good explanation sheets on gerunds and participles.