The secondary indicator is another way to get to the same answer.
At its simplest, the secondary indicator will be another definition (see earlier post - the double definition clue). At its next level of complexity the secondary indicator will require the use of a single technique to get you to the answer. The most complex indicators require you to use a range of different techniques and decode instructions about how to combine them.
In an elegantly written clue, the setter's misdirection should make it hard to spot immediately which part of the clue is the definition and which the secondary indicator.
4. Middle Eastern terrorists on BBC panel show (5)
In this example of a simple charade clue the definition could plausibly be: 'Middle', 'Middle Eastern', 'Middle Eastern terrorists', 'show', 'panel show' or 'BBC panel show'.
Note that the definition will never be *'terrorists' or *'terrorists on BBC' because the definition must start or conclude a clue.
Some common techniques that will be explained in coming posts: