Sorry GabeH.4, you've got the wrong end of the stick here. Gli is used as a plural definite article for masculine nouns beginning with z, ps, gn, s+ consonant, or a vowel. All other plural masc. nouns take i as a definite article.
I know I'm like 3 years late replying to this comment but 'lo' is used before words that start with the letter 'z' or s + a consonant (e.g. lo zucchero - the sugar, lo squalo - the shark). I hope this helps!