What is a focus in witchcraft?

Most people find it easier to focus their mind and hence their energies if the have something to "focus" on.

When working magic practitioners often use a candle or crystal as that "focus". These are not the only things used but are readily available.

When performing Rituals there is often a raising of a cone of power/magic, the focus used to bring several minds into sync can be chanting/singing, dance/movement, a lead meditation (someone leading the group by voice), often in the form of a visualisation (developing a clear and precise mental image of the needed goal).

These are all forms of "focus", there are several others, but these are the most common.