Credits or zombie lane cash are a virtual currency that enables people to purchase special items in games and non-gaming applications. With Facebook you need to use Facebook Credits, you can buy them on Facebook. If you use Google+ you can use Google Checkout to pay directly to the application or game.
On other platforms there are other type of direct payment possible.
The cost of one credits is equal to $0.10 or €0.10, depending on where you live.
Example or getting paid for credits:Edit
You want to buy an in-game item and cost 12 credits.
Facebook: You need to buy 20 credits at Facebook. You can use the credits in the game. If you payed 12 credits in-game, you will have 8 remaining credits. In this example you payed $2 of €2.
Google+: You buy the in-game wanted item directly from the game while using Google Checkout. You just pay the wanted credits. In this case 12. In this example you payed $1.2 or €1.2.
Note: Keep in mind that you still can use the 8 leftover Facebook Credits for something else.
When giving free gifts to neighbors, you can earn respectively an energy drink 5, 200 coins, 5 cash and 1 hotdog. It is possible to send those gifts manually (using the 'add neighbor' button) or with the 'free gifts' button. Quick send here will send maximum of 50 'friends' a gift, and will not check if those play zombie lane or not.
You also get 1 free credit at certain level ups (not all).
Odd calculations and misleading suggestionsEdit
At many places in the game the amount of credits required to obtain a certain item or service is a lot different. You can for instance buy a rope for a mission for 10 credits a piece, buy the same rope from a collection screen at 5 credits, and acquire a rope without using credits from zombies or through a wishlist from neighbors.
With missions the acquired items sometimes are deducted from inventory when requirements are met, but not always. The game regularly is not clear about whether or not items, coins or the like are deducted or not.
Also not at all places the game is very clear about the effect of buying with credits.
At downtown when you have finished City Hall, you can improve the payment of all buildings in downtown. You can ask neighbors to help out, increasing permanently 25% per building in revenue, which can also be paid with 5 credits each. But the mentioned city contracts are a one time only 100% increase without being clearly mentioned as such, and are charged for 3 per contract, with 12 contracts needed at the city hall itself.