Initial sound
The initial sound is morphologically considered the first sound of a word or a syllable . So [ n ] the initial sound of the word "name" or the syllable "Na". And [ ʃ ] ( "beautiful") is the initial sound of the word "school" or the syllable "SCHUMANN".
The initial sound can be followed by an internal or directly followed by an end , as with "you".
Initial sounds, combined with corresponding pictures, are often used in primary school in the form of so-called initial sound tables in the first grades for the acquisition of written language.
Web links
Wiktionary: initial - explanations of meanings, word origins, synonyms, translations