The term 'sight word' refers to any word that is recognised instantly, by sight, whether it is spelled regularly, irregularly, or something in between. The term is often confused with the terms irregular words and high-frequency words.

(LETRS, Lousia Moats & Carol Tolman)

SIGHT WORDS

In various phonics programs, sight words form part of the instruction. ...Sight words are often high-frequency words, labelled sometimes as 'tricky words', that appear a great deal in written and spoken English. There are many varying views on sight word instruction, however, a comprise between these views is:

Sight words are introduced and practiced initially with reference to the sound-spelling correspondences followed by repeated exposure (i.e. whole word memorisation) where necessary. You may need to explain to the students that a given phoneme can be represented in more than one way, something which may seem complicated, however, it sensitises the students to the real structure behind English and how we read.

...it should be made clear that [sight words] are not 'words that can't be decoded' and that they are 'tricky' only because particular sound-spelling correspondences haven't yet been learned.

(The Art & Science of Teaching Primary Reading, Christopher Such)