A Variable can be specified before executing a query on the view. Usually variable values are entered manually by the user on a UI (variable popup). A variable defines a filter on an attribute of the view. Therefore it always has to be assigned to an attribute. The variable values are passed to the engine via the WHERE clause of the SQL statement. Variables are not known by the engine, but only by the clients like Datapreview, MDX, Advanced Analysis for Office or BO Explorer. It is the task of the client to convert the user input into the WHERE clause when accessing the data.
•Parameters or Input Parameters:
A parameter (like a variable) can be specified before executing a query on the view. Usually parameter values are entered manually by the user on a UI (variable popup). A Parameter defines an internal parameterization of the view. This means the engine needs to know it and uses the parameter value during the execution (e.g. to calculate a formula for a calculated measure). The parameter value is passed to the engine via the PLACEHOLDER clause of the SQL statement. A parameter can only have single values. For the end user there is no distinction between variables and parameters. Both appear as input fields on the variable popup.
There are 4 system tables under the schema _SYS_BI which contains information about Variables.
SAP HANA documentation on Input parameters: http://help.sap.com/saphelp_hanaplatform/helpdata/en/d5/c8230abb571014acc592c2c96d92bd/content.htm