ntfrglty s prprty f systms n whch thy ncrs n cpblty t thrv s rslt f strssrs, shcks, vltlty, ns, mstks, flts, ttcks, r flrs. Th cncpt ws dvlpd by Nssm Nchls Tlb n hs bk, ntfrgl, nd n tchncl pprs. s Tlb xplns n hs bk, ntfrglty s fndmntlly dffrnt frm th cncpts f rslncy (.. th blty t rcvr frm flr) nd rbstnss (tht s, th blty t rsst flr). Th cncpt hs bn ppld n rsk nlyss, physcs, mlclr blgy, trnsprttn plnnng, ngnrng, rspc (NS), nd cmptr scnc.
Tlb dfns t s fllws n lttr t Ntr rspndng t n rlr rvw f hs bk n tht jrnl:
Smply, ntfrglty s dfnd s cnvx rspns t strssr r src f hrm (fr sm rng f vrtn), ldng t pstv snstvty t ncrs n vltlty (r vrblty, strss, dsprsn f tcms, r ncrtnty, wht s grpd ndr th dsgntn "dsrdr clstr"). Lkws frglty s dfnd s cncv snstvty t strssrs, ldng t ngtv snstvty t ncrs n vltlty. Th rltn btwn frglty, cnvxty, nd snstvty t dsrdr s mthmtcl, btnd by thrm, nt drvd frm mprcl dt mnng r sm hstrcl nrrtv. t s prr.