observation

n. act of watching; act of looking; act of paying attention; supervision; remark

Observation is an activity of a sapient or sentient living being (e.g. humans), which senses and assimilates the knowledge of a phenomenon in its framework of previous knowledge and ideas. Observation is more than the bare act of observing: To perform observation, a being must observe and seek to add to its knowledge. Observations are statements which are determined by using one of the five senses. Observations aroused by self-defining instruments are often unreliable­¹. Such observations are hard to reproduce because they may vary even with respect to the same stimuli. Therefore they are not of much use in exact sciences like physics which require instruments which do not define themselves. It is therefore often necessary to use various engineered instruments like: spectrometers, oscilloscopes, cameras, telescopes, interferometers, tape recorders, thermometers etc. and tools like clocks, scale that help in improving the accuracy,  quality and utility of the information obtained from an observation. Invariable observation requires uniformity of responses to a given stimulus, and devices promoting such observation must not give out rebellious output as if having "a mind (or opinion) of their own". In statistics, an observation, whether of a sample or the population, measures one or more properties (weight, location, etc.) of an observable entity enumerated to distinguish objects or individuals.
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n. observance, observation, adherence; remark, comment; study

(n.)
The result of an act, or of acts, of observing; view; reflection; conclusion; judgment.
  

(n.)
The information so acquired.
  

(n.)
The act or the faculty of observing or taking notice; the act of seeing, or of fixing the mind upon, anything.
  

(n.)
The act of recognizing and noting some fact or occurrence in nature, as an aurora, a corona, or the structure of an animal.
  

(n.)
Specifically, the act of measuring, with suitable instruments, some magnitude, as the time of an occultation, with a clock; the right ascension of a star, with a transit instrument and clock; the sun's altitude, or the distance of the moon from a star, with a sextant; the temperature, with a thermometer, etc.
  

(n.)
Performance of what is prescribed; adherence in practice; observance.
  

(n.)
Hence: An expression of an opinion or judgment upon what one has observed; a remark.
  

Closely monitoring a patient's condition but withholding treatment until symptoms appear or change. Also called watchful waiting.