Set and Get Session variables in magento

Magento has functionality to create new session variables. You can set it as following

/* Core Session */
Mage::getSingleton('core/session')->setYourVariable('data');
$Data = Mage::getSingleton('core/session')->getYourVariable();

/* Customer Session */
Mage::getSingleton('customer/session')->setYourVariable('data');
$Data = Mage::getSingleton('customer/session')->getYourVariable();

/* Admin Session */
Mage::getSingleton('admin/session')->setYourVariable('data');
$Data = Mage::getSingleton('admin/session')->getYourVariable();