What is the difference between matched and unmatched uncertainties?

[TheJCBand]

I'm beginning to study control theory, and I keep reading about matched and unmatched uncertainties in the literature, but I have yet to find the definitions of matched and unmatched. Could someone explain it to me? Thanks.

 

[ejtopping]

The difference is the equivalency and consistency of the errors in "matched uncertainties".

 

[TheJCBand]

Can anyone elaborate on this? I'd like an explanation in layman's terms.