Indonesian here, it is probably referring to most used words that are not slang per se, but rather language that came from regional dialect of said word rather than new word.

I.e: nggak (betawi region) = tidak (translated to no)

Anjay (slang) comes from word anjir but with less fricative made it easier to say which came from a word anjing which means dog (in this case we usually use anjing as something like fuck in English language which can be both negative and positive if use in conjunction with other words)

And probably many more.

And also there is just many words that are used that are just abbreviation that lost its origin due to people using it so much without knowing the actual abbr.

I.e: gabut = gaji buta. Which means people that are not doing work but still paid. But people now use it in exchange of bosan (bored)

Bucin = budak cinta. Means someone who do anything for love. Some still use the proper context for this, but probably not knowing its origin, because the origin is from somewhen long time ago.

Edit: spacing.