According to the online dictionary:
the (usually) unintentional exchange of letters or syllables between two words or even within a word, often with comic results - especially when the result changes the speaker's intended meaning. The term is named after the 19th century clergyman and academic Rev. William Spooner
William Archibald Spooner
William Archibald Spooner was a famous University of Oxford University don after whom is named a linguistic phenomenon, spoonerism....
, who was supposedly prone to this trait. Among the examples attributed to him is "you've tasted two worms" for "you've wasted two terms".