What is "theory-ladenness"

In the philosophy of science, observations are said to be "theory‐laden" when they are affected by the theoretical presuppositions held by the investigator. The thesis of theory‐ladenness is most strongly associated with the late 1950s and early 1960s work of Norwood Russell Hanson, Thomas Kuhn, and Paul Feyerabend, and was probably first put forth (at least implicitly) by Pierre Duhem about 50 years earlier