The free card is any card that players receive without having to put any chips into the middle of the table. It is a round of betting that goes by without any actual betting. Players essentially pass on wagering so that they can see one more card for free.
There are two sides to the free card: getting and giving. Depending on your hand and your strategy, either of these strategies can be effective. If you have a marginal hand, you will want to get a free card. This can be accomplished by betting in an earlier round of betting, when the amounts wagered are smaller. Usually you must be in last position for this to work. Having opponents check around the poker table to you will give you the opportunity to check yourself and see one more card; hopefully a card that will take your have from marginal to competitive.
Giving the free card is a much different story. This is done to create a false sense of security amongst your opponents. By setting the trap of the free card, you are trying to establish the thought that your hand is not worth betting. This is generally not to your advantage if you have a great hand. If you have a great hand, you will want to get as many bets as possible into the middle so that you can win a greater amount with your monster hands. Giving a free card then is hardly ever a sound strategy, except when you have a hand slightly better than marginal and wish to confuse your opponents.
