Salesforce Trigger Context Variables

Variable	Operators
isExecuting	Returns true if the current context for the Apex code is a trigger only
isInsert	Returns true if this trigger was fired due to an insert operation
isUpdate	Returns true if this trigger was fired due to an update operation
isDelete	Returns true if this trigger was fired due to a delete operation
isBefore	Returns true if this trigger was fired before any record was saved
isAfter	Returns true if this trigger was fired after all records were saved
isUndelete	Returns true if this trigger was fired after a record was recovered from the Recycle Bin
new	Returns a list of the new versions of the sObject records.(This sObject list is available only in insert and update triggers. The included records can be modified only in before triggers.)
newMap	A map of IDs to the new versions of the sObject records. (Only available in before update, after insert, and after update triggers.)
old	Returns a list of the old versions of the sObject records. (Only available in update and delete triggers.)
oldMap	A map of IDs to the old versions of the sObject records. (Only available in update and delete triggers.)
size	The total number of records in a trigger invocation, both old and new.