What is a quadgraph?

Answer 1

A quadgraph is a four-letter spelling pattern (ough is though). The letters together spell one sound. The same is true for a word like weigh. There are only two sounds (w-a). the eigh spells the long a sound.

Graphemes (spelling patterns that represdent a single sound) may be divided into graphs (1 letter - b in bat); digraphs (two letters - ai in rain); trigraphs - dge in judge); quadgraphs.

All an Davies in the UK has written much about this and this is the basis of the THRASS Phonics programme.