Unusual Observation/Outlier - is a data point or an observation that is located far from the rest of the data points. Outliers may be an outcome of variability in measurement or due to an experimental error. All outliers need to be investigated and corrected (usually removed from the data set) as presence of outliers can lead to incorrect statistical analysis.
An application-oriented question on the topic along with responses can be seen below. The best answer was provided by Natwar Lal and Mohamed Asif.
Applause for the respondents- Natwar Lal, Mohamed Asif, Sunil Kant, Ratnakar Bonda and Prabhakar Acharya.
Also review the answer provided by Mr Venugopal R, Benchmark Six Sigma's in-house expert.