yack / yak are similar-sounding terms with different meanings (referred to as homophones). To better understand the differences, see below for definitions, pronunciation guides, and example sentences using each term. 👇
yack: (verb) talk incessantly and tiresomely.
yak: (noun) noisy talk. (noun) large long-haired wild ox of Tibet often domesticated. (verb) talk profusely.
yack: y·AE·k
yak: y·AE·k
(Examples are Wikipedia snippets under the CC ShareAlike 3.0 license. Definitions drawn from WordNet.)