A Platform-as-a-Service development environment created by Salesforce.com, which underlies the core Salesforce CRM functionality and is available as a platform via database.com, as well as via Heroku, a Ruby-on-Rails environment.
Force.com is a cloud based Platform-as-a-Service available for developers to applications hosted in a multi-tenant, cloud based environment with a combination of declarative development as well as through using the native Apex programming language.
Apex is based on Java and can be used to generate custom pages via the Visualforce markup language and components. The platform supports both SOAP and REST APIs for communications with other systems, and provides a database managed entirely through an web based UI, which leverages a query language called SOQL, which is heavily based on SQL.
There is synonym for this tag - force.com.