An aigrette is something that people used to wear on their hats a very long time ago. It's like a fancy decoration that looks kind of like feathers. But instead of being made from feathers, it was made from the feathers of beautiful birds like herons, egrets, and peacocks.
People used to think that wearing an aigrette made them look special and important. But some birds had to be hurt or even killed to get their feathers for the aigrette. This was not nice for the birds, and it made some people very upset.
Nowadays, wearing an aigrette like that is not allowed. It is illegal because it harms wildlife. Instead, people use artificial materials to make decorations for their hats to look beautiful without hurting any animals.