The small marker words — ti, diay, dagiti — that show up in front of almost every noun.
The grammar groups ti, diáy, and words like them as markers — short, closed-class words whose whole job is to introduce a noun phrase. You'll see them constantly, almost never alone.
ti is the plain article. It marks a noun phrase without pointing to a specific one nearby.
ti balásang
the/a young woman
Mangán ti manggá diáy ubíng.
The child will eat a mango.
ti manggá — an unfocused, indefinite goal
diáy is a demonstrative article — it marks a noun as a specific, identifiable one (closer to "that/the" with a sense of "the one we mean"). dagití is its plural: "the (several)."
diáy ubíng
the/that child
dagití ubbíng
the children
Nagtataráy dagití ubbíng.
The children ran away.
Beyond diáy, Ilokano has a small set of demonstrative pronouns for "this/that" that change depending on distance from the speaker and listener — the grammar book distinguishes short forms (like -ay) from long ones (like deytóy 'this', deydiáy 'that').
Deytóy-ak.
I am this.
deydiáy manggá
that mango (over there)
Grammar: Ch. 3.2(g); markers throughout Ch. 4–7, from Constantino's Ilokano Reference Grammar (1971, CC BY-NC-SA 4.0).