serf / surf 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. 👇
serf: (noun) (Middle Ages) a person who is bound to the land and owned by the feudal lord.
surf: (noun) waves breaking on the shore. (verb) switch channels, on television.
serf: s·ER·f
surf: s·ER·f
(Examples are Wikipedia snippets under the CC ShareAlike 3.0 license. Definitions drawn from WordNet.)