what is a blog ?

Let's start with the dictionary meaning of a blog ,

noun

a webpage regularly updated and maintained by an individual or small group, written in an conversational style to make more impressive.

verb

add new information or article , to regularly update a blog.
"it's about a month since I last blogged"

write about an event, situation, topic, etc. in a blog.
"he blogged the geographical and political conventions as an independent"

Now , lets explore more on term "Blog" point wise

Blog is  ...

• Invented in 1994 by a collage student , Justin hall

• A Journal which is updated most regularly by an individual or a group on a web page published on internet

• A Medium to express a thought in constructive way to reach there desired audience in the form of images , texts , videos , graphs , formula's etc.

• Set of posts written by an individual aligned to various subjects such as marketing , business idea's , trading , travel , insurance , loan , web hosting , niche technology , Hollywood , sports , news etc. without violating the content or security policy.

• Kind of website with set of posts arranged in the order with recent article appearing first on landing page

• Opportunity to express the knowledge which can reach to seekers , acknowledged through comments

• An Element to introduce an individual as a blogger or a knowledgeable professional to fulfill their goals

• acts as an interactive feature to convey opinion about a subject , situation and get polled through social networking

• basically structured with header with subject followed by description , main content of the matter , side bars , tag lines , footer , pages etc.

Blog has been evolved from a simple post to complex articles becoming even more powerful with people getting introduced themselves after influenced by other's success as a blogger using readily available blogging tools without any cost. 

Also Read .. How to start earning from Blog using Google Ad-sense