家族類似概念是維根士坦針對傳統哲學中對定義的看法所提出的批判。按照維氏的看法，傳統哲學尋找精確和確定的定義的傾向是建立在一個詞或一個概念當告訴我們它所指稱的，從這意義言，邏輯當建立在形上學上。在用語言時，我們共同的錯誤即要了解一字的意義，我們當對該觀念的本質或屬性有著完整的認識，定義當告訴我們事物如何。維氏指出，一字的意義來自它如何被用，各種不同的用法形成一家族，沒有任何確定不變的意義。與其說有什麼共同的，一字的意義有著家族類似性；複雜、相互重疊、交叉的相似以及不相似。鑒於字的各種變換不定的用法，我們無法在一概念的意義上找到什麼確定的，故字是不可定義的。

　　　　　 The notion of “family resemblance” is one of the ideas with which Wittgenstein criticizes the notion of definition in the traditional philosophies. The tendency to look for sharp and definite definition, according to Wittgenstein, is rooted on the idea that the meaning of a term or a concept is to tell us what the term refers to, hence, logic has its foundation on metaphysics. In using language, the illusion is that in order to understand a word we should have a comprehensive knowledge about the essence or properties of the concept in question. A definition tells how the thing is. Against such an attitude towards definition, Wittgenstein points out that the meaning of a word depends on how the word is used, and the various ways of using a word form a family, i.e. a word can be used without a fixed meaning, it has a family of meanings. Instead of having something in common, the meaning of a word has a family resemblance; a complicated network of similarities overlapping and crisscrossing, and dissimilarities as well. Due to the fluctuating uses of the word, no determinacy may be found in the sense of concept, a fortiori a word is indefinable.