LYNN ? Most dictionaries define the word “stuff” as an informal term for personal possessions or miscellaneous, unspecified objects.No matter what you call it, Americans have a lot of it. In fact, they apparently have too much of it, enough to spawn an entire industry of temporary storage warehouses.According to the Self Storage Association, a non-profit organization representing storage facilities in the U.S., Canada and 18 other nations, the industry has a cap value of $220 billion, and annual revenues of $22.6 billion. It also encompasses 2.2 billion square feet of rental space.Lynn residents need not travel far to find a storage depot. Public Storage at 595 Lynnway and Extra Space at 583 Lynnway are two local options. Both companies also have storage warehouses in Revere and Saugus.In Salem, Uncle Bob’s Self Storage at 435 Highland Ave. is part of a growing corporate chain, while Planet Self-Storage at 39 Medford St. in Somerville has facilities in four states.The Massachusetts Self Storage Association includes many facilities in Essex County, from the corporate chains like Public Storage and Extra Space, to more mom-and-pop varieties like Locker USA in Danvers, and Paradise Self Storage and North Shore Self Storage, both in Swampscott.So what exactly are people storing?In many cases, the warehouse spaces are chock filled with seasonal items like jet skis, snowmobiles, ATVs, even small boats and cars. Storing them inside reduces wear and tear. Businesses, too, are taking advantage of off-site storage for documents and office equipment.According to Planet Self-Storage, customers are not required to tell the facility what they are storing. As the day manager explained, “Different people store different things. There a lots of household items either because they have too many or they are moving and need a place to put everything.”The monthly storage fee depends on the size of the space and can range from about $50 to $400, he said.Tips abound for those planning to put some of their precious possessions into storage. For example, thoroughly vacuum all upholstered furniture because one crumb can attract pests. On that subject, better check the pockets of the kids’ clothing for goodies. Give furniture a coating of polish. Use one or two uniform-sized boxes to make stacking easier. Fill boxes completely to prevent collapse. Seal all boxes. Don’t use large boxes because dishes and books can make for heavy lifting. Number the boxes and keep a corresponding inventory sheet.When packing clothing, forget the mothballs because they stain. If disassembling furniture, stow screws and small parts in a plastic sandwich bag and tape to the piece. Stow small items in furniture drawers. Mattresses and bedding should have covers.Pallets help keep boxes off damp floors. Globes or other items containing water should be emptied to avoid damage by freezing. Soft items like candles can melt when the temperature inside the storage bin climbs. Avoid storing combustibles like paint and thinners. Stand lawn and gardening tools like shovels and rakes in a trash barrel.Seasonal items should be stored near the door to afford easy access, while valuables are best tucked behind furniture toward the rear. Electronic goods and other valuables should be photographed and inventoried. Making an aisle down the center of your possessions also makes for easier access.Industry experts say the most popular reason for renting storage space is to create more usable living space at home. High on the list of stored items are seasonal sports equipment like skis and snowboards, canoes and kayaks, bicycles and motorcycles, holiday decorations, lawn furniture, exercise equipment, extra interior furniture or antiques, keepsakes and clothing – i.e. wedding dresses that often have one-time use but are kept forever.There are approximately 40,000 temporary storage warehouses in the U.S., owned by about 2,000 companies or individuals. The best storage facilities are clean and well