A dummy pronoun is a pronoun used to fulfill a grammatical requirement without providing any real information. The most common dummy pronouns are it and there.
"It is raining."
"There must be a solution!"
"I think it would be fun to go out."
"There's nothing wrong with that."
"Here we go again."
Dummy pronouns are a feature of many Germanic languages, including English, but many languages simply drop pronouns when they are redundant, making the dropping of dummy pronouns one of the common stumbling blocks of ESL learners.
A dummy pronoun may also be called an expletive pronoun or pleonastic pronoun.