[FrankSansC]

From an Intel support page[0] :

  Resizable BAR (Base Address Register) is a PCIe capability. This is a mechanism that allows the PCIe device, such as a discrete graphics card, to negotiate the BAR size to optimize system resources. Enabling this functionality can result in a performance improvement.

[0] https://www.intel.com/content/www/us/en/support/articles/000...