This is the 524th most frequent Malay word.
abu
Ash.
The word 'abu' refers to 'ash', specifically the residue left after something like smoking.
Abu rokok ini mesti dibuang di tempat yang sepatutnya.
This cigarette ash must be disposed of in the proper place.
Here, 'Abu' is used as a personal name, which is a common usage in Malay.
Abu sedang belajar di perpustakaan sekarang.
Abu is studying in the library right now.
In this context, 'abu' means 'ashes', the remains of something that has been burned.