や

Common wordFreq.FrequencyTop 100

Meanings

and; such things as

Listing particle for non-exhaustive examples, often tied to a specific time and place. Softer than と.

as soon as; the minute ...

Follows the dictionary form of a verb; often in the pattern や否や. Literary or formal.

〈物もの〉や〈物もの〉such things as A and B (a non-exhaustive list)
机つくえの上うえに本ほんやノートがある。
There are things like books and notebooks on the desk.
〈動どう詞し〉や、〈事こと〉the moment (something happens), ...
ベルが鳴なるや、生せい徒とたちは教きょう室しつを飛とび出だした。
The moment the bell rang, the students rushed out of the classroom.

とN1sense 1
と lists items exhaustively (this and only this), while や implies the list is incomplete, giving just a few examples.
だ sense 3
だ is the standard Japanese copula, while や is its casual Kansai-dialect equivalent used the same way.
とか
や is a more formal or written-style particle for listing a few examples, while とか is casual and can also add hearsay or vagueness.
たり
や lists nouns non-exhaustively (like 'and' among other things), whereas たり lists actions or states and attaches to verb or adjective forms.
など
や connects items within a list, while など comes at the end of the list to signal that more unmentioned items exist.

The particle や is native Japanese. The interjection and dialectal copula uses are also native, with the copula being a regional variant of だ.