I use the following. I find these definitions to be flexible, inclusive, and consistent with the dictionary:
Method: a way of doing something; an idea or ideas that specify behavior.
Methodology: a system of methods.
Approach: a way of enacting a method; a characteristic pattern that modifies method. E.g. “the stress testing technique may be performed using either a scripted or exploratory approach”
Practice: what somebody actually does; a way of doing something that someone actually uses. (usage note: a method is a practice only in the context wherein someone uses that method)
Process: how something happens; a causally-related chain of events. (usage note: a practice or method may describe or affect a process, but process encompasses the totality of events, not just the parts that people might do or think of themselves as doing)
Test technique: test method; a heuristic or algorithm for designing and/or executing a test; a recipe for a test.
Test strategy: the set of ideas (i.e. methods and objectives) that guide test design and execution.
Test logistics: the set of ideas that guide the application of resources to fulfilling the test strategy.
Test plan: the set of ideas that guide a test project; the totality of test strategy and test logistics. (usage note: A test plan document does not necessarily contain a test plan, and a test plan may not necessarily be expressed in written form. Beware confusing a genuine test plan with a document that merely has “test plan” as its title.)
Testing: questioning a product in order to evaluate it (Bach version); technical investigation of a product, on behalf of stakeholders, with the objective of exposing quality-related information of the kind they seek (Kaner version).
Test Idea: an idea for testing something.
Test: a particular instance or instances of questioning a product in order to evaluate it; or a document, artifact, or idea that represents such a thing.
Test case: see Test