feedback is defined by Oxford Learner's Dictionaries, as an uncountable noun, as "advice, criticism or information about how good or useful something or somebody’s work is" and "the unpleasant noise produced by electrical equipment such as an amplifier when some of the power returns to the system."
Cambridge Dictionary gives "information or statements of opinion about something, such as a new product, that can tell you if it is successful or liked" and "the sudden, high, unpleasant noise sometimes produced by an amplifier when sound it produces is put back into it." Under the labels "engineering" and "specialized" it adds "the return back into a machine or system of part of what it produces, especially to improve what is produced." Its American Dictionary has "reaction to a process or activity, or the information obtained from such a reaction," and its Business English section, labelled "MARKETING, HR," gives "information about something such as a new product or someone's work, that provides an idea of whether people like it or whether it is good."
Dictionary.com lists "a reaction or response to a particular process or activity" and "evaluative information derived from such a reaction or response." Under the label "Psychology" it gives "knowledge of the results of any behavior, considered as influencing or modifying further performance," and under "Biology," "a self-regulatory biological system, as in the synthesis of some hormones, in which the output or response affects the input, either positively or negatively." See also 📝Openness To Feedback.