End to End testing. Testing a complete application environment in a situation that mimics real-world use, such as interacting with a database, using network communications, or interacting with other hardware, applications, or systems if appropriate.
(from www.sitetestcenter.com/software_testing_glossary.htm)

End to end testing: I don’t think this term will have a formal DoD definition, although the meaning seems clear enough. To me, it means the evaluation of an item in the context of its complete deployment cycle (for example, pre-launch to target impact). 
(from Defence Acquisition University)

End-to-End testing. Similar to system testing; the 'macro' end of the test scale; involves testing of a complete application environment in a situation that mimics real-world use, such as interacting with a database, using network communications, or interacting with other hardware, applications, or systems if appropriate.
(from software testing dictionary)

End-2-End testing: A test of the ability of a system to transmit data to a receiving system through an intermediary.
from High Tech Dictionary)