[#Blogged] Developer Edition "DE org"

Development and deployment on Force.com typically take place in an environment or org, which provides a number of features and accommodations for applications within that environment. An environment lets you instantly start developing, testing and deploying your app in the cloud. For an explication of the types of environments, optically discern An Exordium to Environments.
Follwing are the salesforce licenses : 
Salesforce Customer Portal
2 Salesforce CRM licenses
2 Salesforce Mobile licenses
3 Salesforce Platform licenses
5 Salesforce Partner licenses
10 Salesforce Customer Portal Manager licenses  

Other Limits for Developer Edition:
5.0 MB of Data Storage
20.0 MB of File Storage ( attachments)
5000 API requests per 24 hours
Any number of applications
A 500 MB bandwidth and 10 minute service request time limits (per rolling 24 hours) 

Developer Edition (often referred to as a "DE org") is a fully-featured development environment with limits on data and users. Developer Edition is used for:

Trailhead - Salesforce's free and fun online learning tool requires Developer Edition.
Development and Testing - If you don't have a sandbox (a copy of your Salesforce production organization), you can use Developer Edition to isolate development and testing.

ISVs - Independent Software Vendors use DE orgs to create managed packages, which may then be released as apps on the AppExchange.

Developer Previews - Sometimes we release new functionality to Developer Edition before other editions, so you can practice with it.

Fun - You can have more than one Developer Edition, so use one whenever you want to mess around and try something new.

How to signup for free developer edition in Salesforce?

1. Open "http://developer.force.com/".

2. Click "Sign Up" button.
3. Fill in the details. Click "Sign me up". 
4. Verify the account in email.
5. Use "https://login.salesforce.com" for login.