Definition Consonant cluster

Consonant cluster

A consonant cluster in a word is a group of consonants with no vowels between them. The longest possible cluster in English is three consonant sounds at the start, such as 'splash', and four at the end, as in 'twelfths'.

Example 
The tongue twister 'The sixth twisty crisp' has several consonant clusters in it, making it difficult to pronounce.