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 Mohan PB on 8th November 2017.