In corpus linguistics, a collocation is a series of words or terms that co-occur more often than would be expected by chance. In phraseology, collocation is a sub-type of phraseme. An example of a phraseological collocation, as propounded by Michael Halliday, is the expression "strong tea". While the same meaning could be conveyed by the roughly equivalent "powerful tea", this expression is considered excessive and awkward by English speakers. Conversely, a corresponding expression in technology, "powerful computer," is preferred over "strong computer". Phraseological collocations should not be confused with idioms, where an idiom's meaning is derived from its convention as a stand-in for something else while collocation is a mere popular composition.