Reliability of a test means how consistently the test is able
measure a particular characteristic.
A test that yields a similar score when taken by the person
again i.e. he/she repeats it, is said to be a reliable test.
Internal consistency reliability indicates the extent to which
items on a test measure the same thing.
A high internal consistency reliability for a test
indicates that the items on the test are very similar to each other
in content i.e it is homogeneous.
A test is said to have high reliability when it produces
similar results under consistent conditions.For example, if a group
of students takes an aptitute test, you would expect them to show
very similar results if they take the same test a few months
later.