A word or phrase is called pejorative if it is used in a way which implies that something is inferior. Most pejorative expressions may also be used in a non-pejorative way, however, and therefore (as with any implied meaning) determining the intent of the speaker is problematic.
Although pejorative means the same thing as disparaging, the latter term may be applied to a look or gesture as well as to words and phrases.
Sometimes a term may begin as a pejorative word and eventually grow to have a non-pejorative sense. This happened with the terms Yankee and Ham radio operator, which changed from being slang insults to being worn with pride. In other cases, some groups have attempted to reclaim formerly offensive words applied against them, with limited success: In many cases, usage of a term like nigger, redneck, dyke, Kraut, or cripple by someone outside the group is still considered pejorative (and thus offensive).
Conversely, a neutral (non-pejorative) term may grow to become pejorative: The term retarded, to refer to a person whose mental capacity is permanently weak, was originally used as a euphemism to avoid the pejorative senses of words like moronic, feebleminded, and half-witted. But it quickly grew to have a pejorative sense of its own. (It is worth noting that, in its own time, moron was a euphemism for the pejorative word idiot.) This same progression, from neutral to pejorative, may be happening with the words challenged and special, used in the same sense, today. Language writer Steven Pinker has called this process "the euphemism treadmill."
Since meanings change over time, consult an up-to-date dictionary for information on specific words.
See also: List of ethnic slurs