They're latin and generally used as legal terms. They're real words.

Both of those examples are Latin, not English. I don't know the rules well enough to know if foreign words count, even if they're assimilated into the English language.

Correct me if I'm wrong, but I thought words from a foreign language were not allowed in scrabble.......and quid pro quo and et al are Latin, which is, by virtue of not being English, a foreign language

Yes et is allowed, check out this 2 letter word site http://www.mattelscrabble.com/en/adults/tips/tip1.html I do not believe quo is allowed, try this site under the q section http://www.trussel.com/scrabble/rev23.htm#Q

From what I remember about Scrabble, the word has to be listed in the dictionary as it is used in language. If you were playing latin Scrabble, you could use et and quo.

Check the official dictionaries. I keep this site bookmarked: http://www.hasbro.com/games/adult-games/scrabble/home.cfm?page=Dictionary/dict I know et is legal. I'm not sure about quo.

(capitalized words here are not indicative of shouting, but rather are words that refer to Scrabble plays) ET is valid, while QUO is not. The best place to go would be to check the fourth (and most recent) edition of the Official Scrabble Players' Dictionary. The OSPD itself is essentially a mishmash of source dictionaries. I don't know what the exact rules are for a word to be included in the OSPD, but my understanding is that the following rules figure in: 1) It has to be in at least two of the four source dictionaries (the exact dictionaries escaping me at the moment). 2) It cannot be an abbreviation only (i.e. ED is valid on its own, despite being an abbreviation for "education"). 3) It cannot be a word that can only be properly expressed in the source dictionaries as a capitalized word; this is why ZEN is still the most played phony in the game. 4) It must stand on its own. For instance, NUCLEIC is invalid because the word is not used except in conjunction with the word "acid." This rule also excludes the word INASMUCH (as in "inasmuch as"). 5) Acronyms that have crept into the dictionaries on their own may be valid. For example, LASER, SONAR, AMU et al. Of course, no dictionary is perfect, and the OSPD is no exception, but these are the basic rules that I know of for a word's inclusion/exclusion.

Under my house rules, I think words with nothing in the middle should be barred.