qt is the short written form of quart, or quarts. A quart is a unit for measuring liquid (and sometimes dry food), used in the United States and, in an older way, in Britain. On a recipe or a bottle you may see 2 qt, meaning two quarts. Though actually, a US quart and an old British (imperial) quart are not the same size: the US one is a little under a litre, the imperial one is a little over. In Taiwan you will mostly meet litres, so this is a reading word for American recipes and labels, not a word you need to say. There is a completely different qt in the phrase on the q.t., meaning “secretly” — that is not this word.