A hose is a quizbowl question that deliberately punishes a player for having greater knowledge of the topic being asked about in the question. Hoses are considered the cardinal sin of quizbowl questions, as they specifically punish players who possess uniquely identifying knowledge of the correct answer at the time the player buzzed. A player who falls victim to one of these situations is said to have "gotten hosed".
Examples of Hoses
The Classic Hose
...The first well-documented naval battle in history, it took place in 480 BC. (*) The Battle of Salamis saw a victory for what Greek city-state?
A player who buzzes with "Salamis" based on specific knowledge of Salamis at the asterisk will be punished for no reason other than poor question-writing. There's nothing in the question to indicate that it will eventually ask about Athens and it specifically baits players who know their battles into buzzing early. This is a classic hose in that is penalizes players who have a greater degree of knowledge.
The Non-Uniquely Identifying Hose
Another example of a hose is a question that, although it presents factually accurate information, does not uniquely specify the one answer being sought. For example:
...This man argued that AC power should be used over Edison's DC power. (*) For 10 points, name this inventor of a railroad air brake.
ANSWER: George Westinghouse
Someone who buzzes in at the star could reasonably assume that the answer could be Tesla, and in some bad quizbowl formats be ruled incorrect despite the given answer being correct based on the information available.
The Non-Acceptable Identical Answer Hose
Similar to a swerve, this is a question that puts a late restriction on an answer making an equivalent answer incorrect. For example:
....For 10 points, name this type of membrane this allows some kinds of molecules to pass through it while prohibiting others. We are looking for a 13-letter word.
ANSWER: semipermeable membrane
This question is bad because it punishes anyone who buzzes in with selectively-permeable membrane, partially-permeable membrane or differentially-permeable membrane, which depending on the given clues are basically identical terms. Questions that requires certain numbers of letters, syllables, or anything similar are most likely flawed.
...Name a country larger than Monaco in continental Europe (*) that borders just one country.
ANSWER: San Marino
Someone who buzzes at the star here could easily say many other answers that would be correct at the time they buzzed. This is a fundamental problem with non-pyramidal questions: it's often not clear to the player what is specifically being asked for due to the non-pyramidal nature of the question and it forces players to make guesses based not on knowledge of the material but on where the question writer might be going.
The Factually Incorrect Hose
Consider the following question:
...He initiated a crusade against the Catholic Church called Kulturkampf as well as a war with Austria over Schleswig and Holstein. (*) For 10 points, who was the twenty-first president of the United States?
ANSWER: Chester A(lan) Arthur
Anyone who has any knowledge is going to buzz in at or before the (*) mark, say "Bismarck", and be stunned to find out that the question is looking for an American president. In most formats that practice good quizbowl, a reasonably competent moderator would realize that the entire question up to the point of the buzz talked about Bismarck, and just award points to the player who got hosed. However, under the rules of some high school state quizbowl associations, an answer of "Bismarck" would be marked incorrect, and there would be rules designed to prevent coaches from successfully challenging such a ruling.