Amateur astronomers know what the terms "solar system", "galaxy", and "universe" mean, of course. But how often do we astronomers hear these terms inappropriately used? For example, "Wasn't Pioneer 10 the first probe to leave our galaxy?" or "Is the Andromeda galaxy in our solar system?". For me, to tackle these type questions requires an explaination of definitions that risks loosing the attention of the listener amid a trail of astronomical jargon.
In the past I used to cringe at the prospect of answering such questions, because I couldn't present the concepts in a concise comprehendable manner. Encyclopedically rambling off information, as I did, would bore the listener. Equally, using hand gestures to illustrate the relative sizes or distances involved is both awkward and inadequate at public star parties. Pondering this problem one late night hour, about two years ago, I thought of a simple way to explain the terms and have used the following analogy a few times at public star parties. It entertains the listener from a referance that is already familiar and teaches the meanings of the terms "solar system", "galaxy" and "universe" in a way that is easy to remember. This approach can be abbreviated or modified too, dependant on the individual's appetite for it.
Imagine you are standing or sitting in your living room. You see every minuscule detail of your living room from the furniture to the specks of dust on books, shelves and the carpet or floor. Imagine that all these particles of your furniture and living room objects represent stars of various sizes and distances. One speck represents our solar system comprised of the sun, nine planets, moons, comets, etc. Some of the objects or particles are clumped together and represent star clusters. Consider that the other rooms of your house similarly represent stars and clusters of stars. (The walls toward the center of your house can be the dark matter that prevent you from seeing the stars of other rooms). All the rooms combined makeup the entire house. Your house represents our galaxy that we call the Milky Way.
Now imagine that you are looking out the picture window of your livingroom -past the stars of the Milky Way- to the house across the street. You know it is similarly shaped and about the same size as your house, but it appears smaller, because of the immense distance across the street. With rooms and contents inside it, it represents a galaxy all it's own. Other houses down the block also represent galaxies of various shapes and sizes. Some are exotic looking. Some are plain looking.
Perhaps a nearby house is larger than all the others in the neighborhood. It represents the Andromeda Galaxy, the largest spiral galaxy and one of the nearest to us. The local neighborhood comprised of all the houses including yours represents the local galaxies which we call the "local group"; a galaxy cluster.
If you look beyond your neighborhood, perhaps to a distant hilltop, you see another neighborhood composed of more houses. That neighborhood represents a group of galaxies that we call the Virgo Galaxy Cluster. Still countless more distant neighborhoods, that you know exists beyond the hill and in other directions represent more clusters of galaxies.
Scattered in the open country, maybe outside of city limits, are the oldest, most distant objects of all. They are the peculiar objects like quasars and protogalaxies that to this day remain a mystery.
Everything that exists, known and unknown, may be represented by the county or whatever you want to call it, but it is the "everything" refered to as the universe.