Whether it's a Halloween costume you only wore for hours or a major appliance, the old adage that another person's trash is someone else's treasure is the basis for "buy, sell, borrow" Facebook pages.

Typically these sites are limited to a certain community or suburb and they're private, but after an invitation to join the group, you can post an item, list the price and let a buyer know how to get in touch.

Kate Waller says she's made about $500 on sold items, and when it came time to buy baby gear for her little ones, she thinks the savings were immeasurable.

"For example, a swing that you would go to Babies"R"Us and spend $150 on, not joking, perfect condition, I got for $5," Waller said.

Before you try to sell or buy there's a certain lingo.

PPU means porch pick up.

ISO means in search of.

BUMP stands for bring up my post, which puts the post back at the top of the Facebook page to catch more attention.

NIL is next in line.

When someone says an item is cross posted, it means the item is also posted on another sell site.

Also, get to know the rules and regulations of the site so you know what is allowed and prohibited.