What is Machine Learning ?

There is no well define what is and what isn't m/c learning. One of the author Samuel defined machine
learning as the field of study that gives computers the ability to learn without being explicitly programmed.

More recent definition by Tom Mitchell defines machine learning by saying that, a well posed learning problem is defined as follows. He says, a computer program is said to learn from experience E, with respect to some task T, and some performance measure P, if its performance on T as measured by P improves
with experience E.

Let's say your email program watches which emails you do or do not flag as spam. So in an email client like this you might click this spam button to report some email as spam, but not other emails and. Based on which emails you mark as spam, so your e-mail program learns better how to filter spam e-mail.

There are several different types of learning algorithms. The main two types are what we call supervised learning and unsupervised learning.

Supervised Learning : In this we're going to teach the computer how to do something. In supervise learning what's the right answer is already given in training time.

Regression and Classification are Supervise Learning Methods

Regression : Predict continuous value output.
Ex. a) Inventory item store predict how many these items will sell over next month.
b) Predict the price of house according to attributes like as house area and  house locality etc.

Classification : Predict discrete .value output.
a) Examined the mail is Spam or Not.
b) From s/w examined it is hacked or compromised.

Unsupervised Learning :  In this we're going to let it learn by itself. In unsupervised learning what's the right answer in not given at training time.

Unsupervised Learning includes :
a) Clustering : k-means, hierarchical etc
b) Blind Signal Separation :  Principal component analysis, Singular value decomposition etc

Ex. : Divide the news data in multiple categories like as Political News, Cricket News and Bollywood News etc.
Market Segmentation
Social Network Analysis