1. Visible disabilities are disabilities that are generally physical, and are immediately apparent--such as a person who uses a wheelchair, or a person who uses a cane.
2.Invisible disabilities are disabilities that are not immediately apparent. These types of disabilities may be mental or cognitive, and include chronic illnesses such as lupus.
For more information: http://en.wikipedia.org/wiki/Disability, or: http://www.who.int/topics/disabilities/en/
Words to watch out for - words which are not just insults, but have a special social connotation
Fag - used primarily in the West as an insulting term for a gay man. This word can be "reclaimed" in a sense, or used positively in expressions like "fag hag" but in general, it's an expression you should avoid. If someone self-identifies as a fag it's their right, but to most of the community it's an epithet with a long history.
Dyke - used historically as an insulting term for a lesbian. This word has been reclaimed to a greater extent than "fag", with websites like "effing dykes" using it simply as a word for a lesbian, but while it may be appropriate for use in certain settings within the community, it's not a polite term in general.
Tranny - used as an insult for a trans person. Some trans people have started to self-identify as trannies, or use the word in a joking context, but it is still extremely rude and generally just shouldn't be used. It is unfortunately a word that is still heard on television and radio frequently, because of the U.S.'s general ignorance of trans issues.
hermaphrodite - in biology, a hermaphrodite is a plant or animal with reproductive organs normally associated with both male and female sexes. However, it has historically been used to describe people with "ambiguous" genitalia, but it's now considered stigmatizing and misleading, and the term "intersex" is now preferred.
LUG/BUG* - Lesbian Until Graduation / Bisexual Until Graduation - slang terms for someone (usually a woman) who dates the same sex in college or university but will "settle down" afterward with the opposite sex. While this can be a self-identifying term, it is frequently used to disparage women who are seen to be "experimenting" with their sexuality, and is often used as an insult within the gay community. Words like this can be seen as policing people's sexual identities, and so should be avoided.