The property of a system or an infrastructure that can be reconfigured, in which resources can be reallocated, and in which components can be reused or repurposed so that cyber defenders can define, select, and tailor cyber courses of action for a broad range of disruptions or malicious cyber activities.
Sources:
NIST SP 800-160 Vol. 2 Rev. 1
NIST IR 8323r1
from
NIST SP 800-160 Vol. 2 Rev. 1