a similar audience

Yes, but not necessarily.

It really means groups of people who like the same things.

I could sell a product. It might appeal to those who sew or design clothing. These are two similar audiences that would like my product.

When people advertise they have in mind a 'target audience,' the sort of person intested in that product. Put very simply, computer games with lots of shoot 'm up features tend to appeal to teenage boys, so you would advertise them in programmes/magazines/websites that a lot of teenage boys visit.