Difference between feature, feature set and feature vector I learnt that a feature is an individual measurable property of a phenomenon being observed. 
Say for example, I am representing a human being. 
Then various features could be the age, weight, height, etc. Now if I place these features in a vector, a feature vector is formed. From what I have got, the feature vector (an array), in this case will be having three elements-  The first being the age, then weight and finally the height. Similarly for 'n' individuals, I would be having 'n' feature vectors each having 3 elements. 
In this context what is a feature set?
 A: A feature vector is a vector that stores the features for a particular observation in a specific order.
For example, Alice is 26 years old and she is 5' 6" tall. Her feature vector could be [26, 5.5] or [5.5, 26] depending on your choice of how to order the elements. The order is only important insofar as it is consistent.
A feature set is a set of all the attributes that you're interested in, e.g. height and age.
The implicit assumption when using this terminology is that your data is tabular -- somehow, you have chosen to represent it as a "flat", matrix-like format. But non-tabular data formats, like network graphs, video, audio, images, binary data sequences, ... these all require some amount of engineering to represent as feature vectors.
A: Feature: is a list of numbers eg: age, name, height, weight etc., that means every column is a feature in relational table.
Feature Vector is representation of particular row in relational table. Each row is a feature vector, row 'n' is a feature vector for the 'n'th sample.
Feature Set: Help to predict the output variable.
Example: To predict the age of particular person we need to know the year of birth. Here Feature Set = Year of Birth.
Normally good feature set can be identified using expert domain knowledge or mathematical approach.
Hope this will help you. Cheers!!!.

A: From a simple data structures perspective, the difference is that a set has no inherent order and contains no duplicates (c.f. a bag of lottery balls) while a vector has order and may contain any value (similar to an array or one-dimensional matrix).
