A requirement is a description of a software system to be developed, laying out functional and non-functional requirements, and may include a set of use cases that describe interactions the users will have with the software. This is represented by a Jira standard issue record supporting custom issue types as Requirements.
Test Case is a set of inputs, execution preconditions, and expected results (outputs) developed for a particular objective, such as to exercise a particular program path or to verify compliance with a specific requirement. This is represented by a Jira standard issue record with its issue type being 'Test Case'.
Test Plan describes the testing scope and activities. It is the basis for formally testing any software/product in a project. It contains the set of test cases to be executed in the plan. This is represented by a Jira standard issue record with its issue type being 'Test Plan'.
A defect is an identified fault with the software system found while executing the test cases. This is represented by a Jira standard issue record supporting custom issue type as Defect.
Test Cycle is a unique iteration of execution of a Test Plan. Each Cycle will contain the same set of test cases planned for execution in a Test Plan. Each Cycle could be a number of testing passes done on a test plan or be the test passes pertaining to each environment/build it is tested against. It is required to have at least one cycle created to run a Test Plan.
Test Case Run
Test Case Run is a unique execution instance of a given Test Case. This effectively captures the result of testing a Test Case, actual results on each Test Case Steps and create/link defects in support of the findings from the execution.
Test Suite is a logical entity to organize, group, and work with Test Cases.
Tester is a user who is assigned to execute a Test Case, i.e. assignee of a Test Run.