What is defined as the smallest part of spoken language that makes a difference in meaning?

The correct response highlights the concept of a phoneme, which is indeed defined as the smallest unit of sound in spoken language that can distinguish meaning. Phonemes can change the meaning of words; for example, the words "bat" and "pat" differ by just one phoneme, the initial sound made.

In contrast, graphemes represent the written symbols or letters in a language but do not pertain to the sounds themselves. A syllable refers to a unit of sound that typically includes a vowel and can contain consonants, but it is not the smallest unit that differentiates meaning. Lastly, an onset is a phonological term that deals with the initial consonant sound of a syllable, which does not capture the idea of distinguishing meaning on its own. Thus, phonemes are foundational to understanding the nuances of spoken language and play a crucial role in literacy and phonological awareness.