Are these sentences correct or run-ons?
Dogs run in packs; cats are more solitary animals.
When Jeannie got home, her husband was preparing her favorite dinner.
No, they're not run-ons. They are both correct.
The first sentence, "Dogs run in packs; cats are more solitary animals," is correct. It is written as two independent clauses connected by a semicolon. This usage is known as a compound sentence.
The second sentence, "When Jeannie got home, her husband was preparing her favorite dinner," is also correct. It is written as a complex sentence, with a dependent clause ("When Jeannie got home") followed by an independent clause ("her husband was preparing her favorite dinner"). The comma is used to separate the dependent clause from the independent clause.