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: 
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.
Condos tend to be in complexes rather than single buildings. Additionally, a condo is purchased and owned, whereas an apartment is rented.

[This Link](http://www.realtor.com/Basics/AllAbout/HomeAffordability/Condo.asp) has some good info about condos.