The phrase "inbuilt memory" refers to the storage capacity that is already built into a device, such as a computer or smartphone. It is the space where information and data are stored, including files, photos, apps, and more. Full definition
It packs 4 GB RAM and 64 GB inbuilt memory along with expandable storage support up to 256 GB via microSD card. (indianexpress.com)
This is very unlikely of Google since the Nexus phones always came with inbuilt memory with no option for a memory card, mostly the listing is wrong or Google is planning to surprise us in a rather big way. (techpp.com)
The ASUS Zenfone 3 Max (ZC553KL) comes with 32 GB of inbuilt memory which can be expanded further up to 128 GB by using a microSD card. (gadgetguide4u.com)