What is the space between Galaxies?
That' a bit like asking what is the distance between cities! But, even the closest galaxies to us are on the order of about 100 000 light years to several times that value.
The distance to other galaxies in our universe differs immensely! Those that are "very close" to us are still 100 000 light years away or more. Since a light year is roughly 9 trillion km, we are talking a long way!
The observable universe is far greater than this however, and measures billions of light years across. we know that the universe has been expanding for 13.8 billion years, and at an increasing rate, so that's a lot of space.