A defenition in resaech technics

Definition
You are probably thinking of the Heisenberg Uncertainty Principle which states that the mere fact of being watched, for example, alters the nature/behavior of what is being watched.

Actually, that's an almost universal mininterpretation of Heisenberg. Heisenberg basically stated that you can measure the position or momentum of a subatomic particle to some degree of precision, but you cannot measure both at the same time as the measurement of one interferes with the other. He derived this from previous work by Einstein and Planck showing the dual wave/particle nature of matter (as well as light).

Macroscopic events are relatively easy to observe without altering them.

Actually I have a feeling that Glitsa is referring to 'The Experimenter Effect'.
Where the experimenter actually influences the outcome of an experiment because they either believe the results they get or do not.
A case of this is in the paranormal areas of research where experimenters who believe in the effects they are looking for are several times more likely to get positive results than experimenters under the same conditions who do not believe in the paranormal.

The experimenter effect has been measures in many areas of research including hard physics.