"Internal storage" refers to a built-in space within electronic devices, like phones or computers, where data and files are stored. It's like a digital filing cabinet inside the device. Full definition
It offers 16 GB of internal storage out of which 10 GB will be reserved for the users and rest being taken up by the OS which is expected to be Android Nougat. (themobileindian.com)
What's more, it comes with 64 GB of internal storage space which can be further expanded by up to 2 TB. (flipkart.com)
The phone comes with 32 GB of internal storage with expandable memory of up to 256 GB. (techtimes.com)