What is the historical cause of the disparity between spelling and pronunciation known as?

The historical cause of the disparity between spelling and pronunciation is known as orthographic depth. This refers to the degree of consistency between the spelling and pronunciation of words in a language. Languages with shallow orthographies, such as Italian or Finnish, have a high degree of consistency between spelling and pronunciation, while languages with deep orthographies, such as English or French, have a lower degree of consistency. This can be attributed to various historical factors, such as language changes, borrowing of words from other languages, and the influence of dialects and regional variations.

The Great Vowel Shift