It's an indefinite pronoun, similar to the English "someone" or "somebody," and is used to refer to a person whose identity is unknown or unspecified.
Here are some examples of how it's used:
* Jemand hat geklingelt. (Someone rang the doorbell.)
* Ich suche jemanden, der mir helfen kann. (I'm looking for someone who can help me.)
* Jemand muss den Fehler gemacht haben. (Someone must have made the mistake.)
It's important to note that "jemand" is always singular, even if it refers to multiple people. If you want to say "some people," you would use "manche" or "einige."