What are trigraphs?

Trigraphs are indeed defined as three-letter combinations that create a single consonant sound. This means that when these three letters are put together, they function as a collective unit to produce one specific sound, much like a digraph does, but involving three letters instead of two. For example, the trigraph 'tch' in the word 'catch' represents a single sound, the 'ch' sound, allowing for an understanding of how certain letter combinations relate to phonemic expression in language.

The other options do not accurately describe what trigraphs are: combinations of two letters making a sound refer to digraphs, while sets of three vowels in a word or four-letter words do not capture the concept of trigraphs at all. Understanding trigraphs is essential for decoding and encoding words in literacy instruction, particularly for students who struggle with phonological awareness and spelling.