Question: I have never really understood the connotation of someone calling their domicile a *condo* over the word *apartment*. I have a vague feeling the former is fancier and more up-scale, but are there any real differences I'm not aware of?

Answer: 
In the US, a [condominium](http://www.merriam-webster.com/dictionary/condominium) involves an investment of funds, and is similar to buying a house. A person actually owns a condominium and can sell it for a return on investment. Also, they can use it as collateral for borrowing money.

An [apartment](http://www.merriam-webster.com/dictionary/apartment) is rented/leased from a landlord/landlady. Rental payments go to the owner, and the tenant does not own the property, so cannot borrow against it. When a person moves out of an apartment, they may receive their security deposit back, but that's about it.

I think owning a condo probably is considered more high-class than renting an apartment. Many, many rich people in New York City own condos, for instance, and brag about it.
A *condominium* does not describe housing. It is strictly a form of ownership and is a legally defined term. All states have acts that define what is a condominium. An office building, a mall, anything can be a condominium.

Moreover, a residential condominium can take any form: an apartment, a townhouse, a free-standing structure (among others), etc. I work on a development that had a highrise building, a mid-rise building, townhomes, and a small store, and all of them were legally structured as condominiums. Again, *condominium* only describes the structure of ownership.

The term *apartment* describes any unit, among many others contained in one structure; it is a unit "apart" from the others. It does not matter whether these units are rented, owned, or cooperatives, or a mix. Think of this, if apartments were dwellings for rent, then the phrase *apartment for rent* would be redundant, but it is not.

In conclusion, a *condominium* is a ownership structure (along with free-hold and cooperative) and an *apartment* is a descriptive term.