Phoneme

A single distinctive sound in a language

Morpheme

The smallest grammatical unit of speech. It may be an entire word (cat) or an element of a word (re- and -ed in the word reappeared).

Dialect

A regional variety of language distinguished by features of  vocabulary, grammer, and pronunciation from other regional varieties and constituting together with them a single language

Idiolect

The language or speech pattern of one individual at a particular period of time.

Grapheme

A letter in the alphabet, a mark of punctuation, or any other individual symbol in a writing system. <.>

Minimally different

Cats-Hats

Maximally Different 

Cats-Moods

every phoneme is different

Orthography

The customary or "correct" pronuciation of words.