Add a New system variable in Magento

Using SQL:  

INSERT INTO `cmsdb_name`.`core_config_data` (
`config_id` ,
`scope` ,
`scope_id` ,
`path` ,
`value`
)
VALUES (
NULL ,
'default',
 '0',
'design/footer/terms_condtn_txt',
'terms and condition text here' )

Using PHP:

$terms_condtn_txt = Mage::getStoreConfig('design/footer/terms_condtn_txt');