What is molecular weight cut-off (MWCO) of a membrane?

The molecular weight cut-off (MWCO) of a membrane is a crucial parameter used in filtration to denote the pore size distribution and retention capabilities of membranes. It provides insight into the ability of the membrane to retain more than 90% of a solute with a known molecular weight. MWCO is measured in Daltons (Da) or Kilodaltons (kDa) with 1 kDa equal to 1000 Da.