As question explains, I did a search on the web and didn't find a suitable answer, even in wikipedia.
Can anyone please explain it to me?
Corporate identity is one of those vaguely defined, hodge-podge ideas that grows in scope as more consultants from different disciplines try to mark out their own piece of the market.
From a designer's viewpoint, "identity" is all the ways people identify the company visually: how it looks to the world. A common misconception, particularly among owners of small businesses, is that it's just the logo, but of course it's a lot more. To keep it simple, I'm limiting everything here to what a graphic designer will work on.
You can develop an "identity program" for an entire company, a particular product line, or even a single advertising campaign. All of these are "corporate identity."
The simplest sort of identity program would be a logo (if they don't have one already), signage and stationery designs. At a minimum this includes an exact color palette, typefaces for correspondence and advertising, paper type and color.
Depending on the size of the company and the budget, a basic identity program should include a style guide that lays out exact uses for the logo (absolutely essential if it's a trademark), what variations, if any, are allowed or required (there may be one version for small sizes, one for larger, for example), and examples of prohibited uses. It must say exactly how the logo will be reproduced in print, on the web and in video, how big it must be in relation to context, required white space around it and very exactly defined colors.
If the company has a slogan or tag line that appears in conjunction with the logo, the style guide must specify its position and size in relation to the logo itself and a clear statement of when it should and should not be used. This would be the minimum, and is for use not only in-house but for media people who may want to show the logo in connection with an article. It should have specifications for corporate communications -- letters, invoices, etc. -- that specifies margins, line spacing, typeface, address placement, greeting line, etc.
Marketing collateral is defined in the style guide as part of any identity program. The style and quality of photography, overall style, use and style of line art or illustration, typefaces, color palette, paper stock for print and so on are part of corporate identity (especially in connection with a single ad campaign). These specs would include the web, interactive and mobile presentation, TV and video where applicable.
Needless to say, a style guide may be anything from a few pages to several inches thick. A corporate identity includes everything in it plus whatever the brand consultant or in-house brand management say it includes. As a designer, you only have to worry about the visuals.
When you work with a client that already has an identity program, be sure to get a copy and study it. Stay within the guidelines if you want to turn them into a steady client and avoid expensive problems.
Wikipedia says it all but don't know what is hard in it for you...
To begin with, it is important to know that the corporate identity, just as individuals’ personality, is the image with which your company can be identified. A company’s corporate identity is the group of attributes and values a company has: its “personality”, its reason of being, its spirit and soul. The image reflected by the “company’s personality” will make the company identifiable and different from the rest and it will also determine its importance in the business world. Corporate identity is the group of pieces, aspects, ideas, methods and techniques that your brand needs to be identifiable. Your company’s corporate identity can be formed by many of the pieces that form a communicational style: logo, letterhead, business cards, folder, inserts, envelope, etc.
hope this will help...